Democrats have religiously deferred to special counsel Robert Mueller over the last 17 months, hamstrung by their lack of congressional power and expressing faith that the respected investigator will get the job done if left alone.

That could all change after November.

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If Democrats retake the House in the midterm elections, they’re prepared to use their newfound subpoena power to aggressively open probes into President Donald Trump’s finances and connections to Russia. But doing so — just as Mueller appears to be entering the final laps of his own probe — would create tensions between the special counsel and a newly-crowned majority party replenished by scores of freshmen lawmakers who rode into Capitol Hill on an anti-Trump wave.

House Democratic aides have been meeting informally in recent months to discuss ways to do their jobs while avoiding stepping on Mueller’s toes in 2019, even toying with the idea of calling the special counsel in for a private bipartisan briefing.

“The House may want to start their oversight by bringing in special counsel Mueller to hear from him,” said former California Rep. Henry Waxman, who chaired the House Oversight Committee during the final two years of the George W. Bush administration and has been meeting informally with House Democrats to discuss investigation strategies.

Potential conflicts could come on many fronts. For starters, Democrats will be eager to see Mueller’s findings and will be hard-pressed to give him space if he’s not finished yet. If Mueller’s Justice Department supervisors resist making the special counsel’s work public, a clash could emerge.

Perhaps most potentially disruptive: Democrats could cause Mueller problems if they start granting immunity to witnesses who the special counsel still wants to question or prosecute.

“It’s something that I think we have to handle with great care,” House Minority Leader Nancy Pelosi (D-Calif.) conceded last week during a Harvard University event.

“We won’t interfere,” the potential next House speaker added. “We shouldn’t. We won’t. But we do have to have one thing that we should all agree on: The truth for the American people and where the truth leads us is another thing.”

Pelosi’s pledge is easier said than done, though, with early signs that the two sides could overlap just as Democrats gear up for an open 2020 presidential primary season.

Democrats on the House Intelligence Committee earlier this year released a “partial list” of more than 70 people, organizations and companies they said Republicans refused to fully pursue as part of their Russia investigation.

California Rep. Adam Schiff, the likely new chairman of the panel if Democrats win power in November, has signaled plans to focus on that unfinished business, including hearings on suspected money laundering at the Trump Organization and issuing a subpoena for communications between the president and his oldest son, Donald Trump Jr., surrounding a 2016 meeting with a Russian attorney who was promising to deliver dirt on Hillary Clinton.

On the House Judiciary Committee, Democrats poised to begin impeachment proceedings have offered up an oversight road map that signals potential conflicts with Mueller. In August, they called for a Justice Department briefing to glean more details about former Trump personal lawyer Michael Cohen’s guilty plea and the allegations that Trump directed him to break campaign finance laws. They’ve also called for an examination into Trump potentially abusing his pardon power, as well as his associates implicated in crimes from the Mueller investigation.

It’s not known to what extent Mueller is probing these areas, but Democrats concede that poking around could inadvertently draw out the special counsel’s own investigative interests far sooner than the special counsel might like.

“It’s a problem I’d like to have one day,” said a senior House Democratic aide.

Come January, Democrats say they will reassess their oversight plans based on the election outcome and to take into account whatever stage Mueller is at in his investigation. They’ll also need to consider whether Attorney General Jeff Sessions and Deputy Attorney General Rod Rosenstein remain in their jobs. Trump has signaled interest in changing up his DOJ leadership, a move that would mean new oversight of the special counsel’s investigation.

If history is any guide, an aggressive Congress and the Justice Department don’t always get along, especially when there’s an independent counsel involved.

Already, there are ongoing disputes between Trump-allied Republicans on Capitol Hill and the Justice Department over documents and briefings tied to the origins of the government’s Trump-Russia investigation.

Further back, in 2008, Democrats — led by Waxman — argued that President George W. Bush thwarted their investigations into the leak of a covert CIA officer by invoking executive privilege in response to a subpoena for Vice President Dick Cheney’s testimony to the FBI.

And during the investigations into the Reagan administration’s secret sale of arms to Iran, Congress’ decision to offer immunity in exchange for testimony from retired Marine Corp. Lt. Col. Oliver North and Reagan national security adviser John Poindexter drove a federal appeals court to vacate the two officials’ convictions.

The Watergate scandal was a rare example of the judicial and congressional branches working in tandem. Special prosecutor Leon Jaworski in 1974 even sent a road map of his work with a federal grand jury to the House Judiciary Committee, which helped pave the way for impeachment proceedings and President Richard Nixon’s resignation.

Not all legal experts believe having Congress put its stamp on work that’s simultaneously part of an active law enforcement probe is a bad thing.

“Being supportive of an investigation doesn’t in the end mean deferring to the criminal investigators,” said John Q. Barrett, a former associate counsel who worked under independent counsel Lawrence Walsh during the Reagan-era investigation into secret U.S. arms sales to Iran. “When you’re the minority and powerless to do the investigation, then it’s easy to be cheering for the Justice Department investigation. But when you’re the majority and doing your own House investigation, you may well butt heads.”

Douglas Letter, a recently retired senior DOJ attorney who teaches at Georgetown University Law School, noted that Congress and Mueller have “totally different goals.”

The congressional investigation is designed to give the American public a report on what happened in the 2016 election and “whether there’s anything political that can be made of it,” he said. Mueller, in the meantime, is a criminal investigator whose job is to identify crimes and prosecute them.

But Republicans will be quick to pounce on the earliest whiff of oversight overreach. They’re primed to point out changes in tone from lawmakers who have been deferential to the Justice Department. Schiff, for example, has been insistent that DOJ shouldn’t give up information about core parts of the Mueller investigation.

“If the shoe is on the other foot in a month and a half, let’s see if he stays consistent,” said William Moschella, the former head of Justice Department legislative affairs office during the George W. Bush administration.

Trump allies slammed Pelosi earlier this week after she said during a CNN event that subpoena power was “a great arrow to have in your quiver in terms of negotiating on other subjects. ”

“This is what they do in Third World countries. Disgusting concept and a slippery slope that America wants no part of,” Eric Trump wrote on Twitter.

“It’s about politics for them,” Mark Corallo, a former spokesman for the Trump personal legal team and the Bush DOJ, told POLITICO. “If they think there’s political advantage to stepping on the special counsel’s toes, they’ll do it.”

Most believe, though, that the Democrats will hold back from causing problems for Mueller, at least for a few months, if they take the majority. Some predicted that Democrats could even try to strike an arrangement with the special counsel to let his team operate for six months or so without significant congressional pressure.

For Democrats, though, that’s a short window before other demands do start taking over, said Paul McNulty, a former George W. Bush deputy attorney general.

“There won’t be any purchase of a long-term peace,” he said.