Acting Attorney General Matt Whitaker is only one day into the job and already he looms large over special counsel Robert Mueller’s investigation.

Tens of thousands of activist-organized protesters gathered at 900 events across the country on Thursday night — including in Times Square and in front of the White House — calling on the new head of the Justice Department to recuse himself from the Russia inquiry because of conflicts of interest.

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The outspoken husband of White House senior counsel Kellyanne Conway co-authored a New York Times op-ed deeming President Donald Trump’s appointment of Whitaker — to replace the fired Jeff Sessions, for whom Whitaker served as chief of staff — as unconstitutional.

On Capitol Hill, House Democrats still in celebratory mode after winning back majority status in Tuesday’s midterm elections convened an emergency conference call to discuss plans to investigate Sessions’ ouster when they have gavels and subpoena power in January.

Whitaker’s promotion even surfaced at the start of a federal court hearing in Washington, where an appellate judge presiding in a case that centers on the legality of Mueller’s appointment told lawyers representing the special counsel and a former aide to longtime Trump adviser Roger Stone that they should plan to file supplemental briefs that address the change in command atop the Justice Department.

To Whitaker’s critics, the newest member of the Trump boogeyman club is an inexperienced but loyal acolyte installed as Mueller’s new supervisor to make under-the-radar moves designed to protect the president. They pledged to be vigilant in watchdogging him.

“There are no secrets,” said Norm Eisen, the former top ethics official in the Obama White House. “If he steps out of line, it’s going to become known.”

Trump’s allies countered that Whitaker was a welcome new face replacing Sessions, whose own recusal from overseeing the Mueller investigation and all other matters tied to the controversial 2016 election has long frustrated the president.

“Terrific!” John Dowd, the president’s former personal attorney, said in an email to POLITICO when asked for comment about Whitaker’s appointment.

Trump’s current team of lawyers insisted on Thursday that the appointment of a new attorney general would not affect the way they interact with the special counsel.

“I think that any rational decision maker would come out the same way on this as a lawyer, so I don’t know how much difference it makes,” Trump attorney Rudy Giuliani said in an interview.

Under DOJ regulations governing his position, Mueller is actually not subject to daily supervision from anyone in the department.

But Whitaker, who before joining Justice made dozens of public comments critical of the special counsel appointment, has now picked up veto power for some of Mueller’s most important moves.

For starters, Whitaker can ask the special counsel for explanations on any investigative or prosecutorial steps, and he has the authority to overturn anything Mueller does if he deems it “so inappropriate or unwarranted under established Departmental practices that it should not be pursued.”

Whitaker’s new role means he is primed to have immediate influence over Mueller ahead of key court dates involving cooperating government witnesses, including former Trump campaign chairman Paul Manafort (a pre-sentencing status report is due Nov. 16); former Trump personal attorney Michael Cohen (a sentencing date is set for Dec. 12 in a case in federal court in New York referred by Mueller’s office); and former national security adviser Michael Flynn (a sentencing date is set for Dec. 18.).

The new acting attorney general is also positioned to weigh in on a topic central to the president who just appointed him: whether Mueller can subpoena Trump and force his testimony.

Giuliani on Thursday said the president and his lawyers were scheduled to have a critical meeting next week to discuss whether to respond in writing to a first round of written questions. Once that decision is made, Trump’s attorneys and the special counsel can re-engage in negotiations over a sit-down interview that would cover topics related to Trump’s time in the White House — including the May 2017 firing of FBI Director James Comey that spawned a probe into whether the president committed obstruction of justice.

No subpoena has been issued for Trump’s testimony yet, but Giuliani said that talks with Mueller on the topic could still break down and result in a high-profile legal fight. “We both agreed to leave it open to discussion,” the president’s lawyer said.

Whitaker has final say over major Mueller moves involving indictments. And while those kinds of actions have largely remained under wraps until they are unsealed in court, several members of the president’s inner circle of longtime aides, associates and family members, including Stone and Donald Trump Jr., remain in the crosshairs.

The acting attorney general will also have an important role in Mueller’s end game. The special counsel at the end of his work must submit to Whitaker a confidential final report explaining why he chose to bring charges against some people but not others.

A decision on whether to make that report public will rest with Whitaker.

“I can see a scenario where somebody who may perceive his loyalty more to Trump than to the department and the public deciding the report is in and it’s sealed,” said one former top Justice official in the Obama administration. “Just like the Watergate report. It’d be available in 40 or 50 years.”

Whitaker can’t totally stifle Mueller.

The DOJ regulations also require the acting attorney general at the end of the Mueller investigation to issue a report to the chairs and ranking members of the House and Senate Judiciary committees spelling out any major moves the special counsel wanted to make but that got vetoed.

“He’ll have to take the heat for those if it looks like those were politically motivated,” said Mary McCord, a Georgetown University law professor and former DOJ official who helped oversee the FBI’s Russian-meddling investigation before Mueller’s appointment in May 2017.

Trump, of course, has been no fan of the Mueller inquiry since its start. During his post-election press conference on Wednesday, the president mused about his power to end the investigation if he wanted to. “I could fire everybody right now, but I don’t want to stop it because, politically, I don’t like stopping it,” Trump said.

But with Whitaker now atop the Justice Department, one less-noticeable way to meddle with Mueller would entail repealing or rewriting the underlying DOJ regulations in a bid to shutter the special counsel’s work or to eliminate the requirement for congressional notice whenever he’s overruled.

“In this administration nothing would surprise me,” the former senior Justice official in the Obama administration said. “They’ve already proven themselves to use tactics that you don’t see in the United States.”

A DOJ spokeswoman declined comment on Thursday when asked whether Whitaker had any plans to rewrite the underlying special counsel regulations.

Before joining the department, Whitaker suggested during a CNN interview that one way to stymie Mueller was for a new attorney general who replaces Sessions to reduce his budget “so low that his investigation grinds to almost a halt.” But that train may have already left the station — at least for the next 10-plus months, because Mueller got approval back in July from Deputy Attorney General Rod Rosenstein for his spending through the end of the current fiscal year.

For now, Mueller appears to be full steam ahead — no matter who’s atop DOJ.

On Thursday, Deputy Solicitor General Michael Dreeben, who represents Mueller’s office, argued in federal appeals court that Mueller’s supervision was one of the critical elements backing up why his appointment is constitutionally sound.

“It’s not the case that the special counsel is off wandering in a free-floating environment and can decide when to report,” Dreeben said during oral arguments in the case, which centers on a Mueller subpoena to compel testimony from Stone’s former aide Andrew Miller.

Also Thursday, the special counsel’s office appeared to file a 12,970-word sealed brief, a sealed motion and a sealed supplemental appendix in federal appeals court in a mystery case involving a different fight over one of his grand jury subpoenas.

Sessions’ status atop the Justice Department had long been tenuous. And some observers say Mueller appears to have been operating with that in mind, noting his moves to hand off some of his work to other U.S. attorneys around the country.

Jon Sale, an assistant special prosecutor during Watergate and a close friend of Giuliani’s, said he expected that Mueller had prepared for possible meddling from above by interviewing witnesses with FBI agents in the room, rather than bringing them before a grand jury where the testimony is more difficult to share. He also said the special counsel could have filed both sealed indictments and grand jury reports in federal court, where a judge would have the final say on their release.

“I have no doubt the people in Mueller’s office have a contingency plan,” Sale said.

Politically, Whitaker has become a launching pad for Trump critics, who on Thursday used his appointment as the rallying cry for a mass protest organized to support the Mueller investigation.

“We’ve always conceived of this as a show of opposition and a deterrent force to make noise if something like this did happen,” Leah Greenberg, one of the former House Democratic aides who co-founded the liberal anti-Trump network Indivisible, said in an interview about the protests.

Indeed, the Sessions-Whitaker shakeup was front and center as protesters gathered from Dayton, Ohio, to the Boston Commons. Two of their hashtags — #NoOneIsAboveTheLaw and #ProtectMueller — were trending on Twitter.

Elana Schor contributed to this report.

Ten Democratic incumbents or members-elect told POLITICO that they will vote against Nancy Pelosi for speaker on the House floor, exposing a serious problem for the California Democrat in her bid to reclaim the gavel.

Eight sitting lawmakers or their offices said on Thursday that they will oppose Pelosi on the floor. Two candidates who won on Tuesday previously said the same.

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That’s an issue for Pelosi, who has led the Democratic caucus for 16 years, and significantly narrows her margin for error in her bid to lock down the 218 votes needed to return to the speakership.

Pelosi’s office dismissed the notion that she wouldn’t get the votes to be speaker. And her allies note that she has two months to win skeptics and said she plans to take her fight all the way to the floor.

“Leader Pelosi is confident in her support among Members and Members-elect,” said Pelosi spokesman Drew Hammill. “Democrats don’t let Republicans choose their leaders. The election proved that the GOP attacks on Pelosi simply do not work.”

It’s going to be close at the very least: Without every race decided, Democrats have picked up 31 seats in the midterm elections for a total of 226, meaning Pelosi can lose eight votes on the House floor. However, Democratic leaders believe they’ll net another half-dozen seats that have yet to be formally called, meaning Pelosi could lose up to 14 members.

Meanwhile, the anti-Pelosi faction — whom some have dubbed the “revolutionaries” or the “rebels” — are working to grow their numbers. Eight of them joined an hour-long conference call Wednesday night to discuss strategy and messaging. They’ve divvied up the names of just-elected candidates who have called for “new leadership” and are reaching out to encourage them to vote against Pelosi on the floor.

These members’ pitch to incoming lawmakers is this: You’re not alone.

The Pelosi critics are arguing that they may be able to deliver as many as a dozen incumbents to vote against Pelosi on the floor, and that they could be successful in ousting her should these incoming freshmen join forces.

The eight lawmakers or offices who have confirmed to POLITICO that they intend to vote against Pelosi on the floor are Democratic Reps. Ed Perlmutter of Colorado, who organized the Wednesday night call, Kathleen Rice of New York, Seth Moulton of Massachusetts, Bill Foster of Illinois, Tim Ryan of Ohio, Filemon Vela of Texas, Kurt Schrader of Oregon and Rep. Conor Lamb of Pennsylvania.

The campaigns of Reps.-Elect Abigail Spanberger and Jason Crow have told POLITICO their bosses won’t vote for her on the floor. Pelosi critics say there are more to come, but until these members publicly say so, it is unclear if they will follow through.

This list does not include two Democrats who voted against Pelosi in 2016: Reps. Jim Cooper of Tennessee and Ron Kind of Wisconsin. Neither office has returned request for comment about whether they intend to do the same again.

Pelosi has been working behind the scenes to lock down support and is already making some headway. Two lawmakers have removed their names from a letter calling for rules changes that would make it more difficult for her to become speaker. One of those, Rep. Robin Kelly, told POLITICO that she will support Pelosi on the floor.

“I do think you need an experienced person at the top to help get that together, get us organized and start off on the right foot as we get back to work for the American people,” Kelly said.

The other lawmaker who removed his name, Rep. Albio Sires of New Jersey, did not respond to a request for comment.

But Pelosi has also won over another former critic, Rep. Sean Patrick Maloney of New York, who released a statement Thursday night saying he backs her: “The new Democratic majority must deliver results for the American people. I am convinced that at this critical moment, Nancy Pelosi remains the right person for the job.”

Pelosi allies are hoping to convince some of the incoming lawmakers to oppose her in a secret ballot caucus vote, where she only needs half the Democrats to win the nomination, and then vote for her on the floor. There’s also been talk of having some vote “present” or skip the vote to pad her margin.

Schrader, who was working Thursday afternoon to organize a call with the new freshman class, said these candidates would be foolish to do so and that it would open them up to political attack ads in 2020.

“If they say they’re not going to vote for Pelosi on their campaign, then they turn around and do that… I think that’d be a foolish exercise for them, and I’m just trying to advise them on the smart thing to do,” he said.

Indeed, Ryan has also been encouraging the group of rebels to frame the issue as a matter of protecting the majority: these members said on the trail that they would back new leadership or won’t back Pelosi. They’re likely to be attacked by Republicans in the future if they flip-flop.

As if on cue, the Republican National Committee on Thursday taunted Democratic winners about whether they would keep their word.

“Which House Democrats will break this critical promise to their constituents as their first official act?” read an email that listed all the Democratic candidates who called for “new leadership” or said they would not back Pelosi.

According to anti-Pelosi organizers, the lawmakers willing to vote against her have discussed putting their names on a letter saying that they will be a no on the House floor. They ultimately decided to postpone that plan and instead work to grow their numbers first.

However, the group agreed on the call Wednesday night that they would propose the rule — a requirement that the speaker nominee receive 218 votes in caucus as well as on the House floor — as early as next week: first, in a caucus meeting with current members, and then again in a separate caucus meeting with new members-elect. Currently, Pelosi only needs support from half the caucus to get the nomination

The rebels’ biggest problem is this: They don’t have someone to challenge her, and as Pelosi allies like to say, “You can’t replace someone with no one.”

Some Pelosi critics had encouraged Rep. Hakeem Jeffries of New York to run for speaker, but Jeffries declared Thursday for the No. 4 House post, caucus chair. Ryan, who unsuccessfully challenged Pelosi in 2016, has said he’s not currently looking to run, though he didn’t rule out doing so.

Schrader acknowledged having a challenger would help their cause since some members feel more comfortable voting for someone rather than simply voting against Pelosi. But Schrader said he understands why no one has jumped in due to the intense backlash the person may face for going up against the most powerful lawmaker in the caucus.

“That person becomes the focus of the discussion… gets beat up badly … and it gets to be pretty ugly pretty quick,” he said. “The main message is: ‘Anybody but her.’ Then, it opens up a much friendlier, better discussion about the talent we have in our caucus.”