House Democrats, with their new majority, will have an expansive new toolkit once they take control of the chamber on Jan. 3 to protect special counsel Robert S. Mueller III’s investigation — even if acting Attorney General Matthew Whitaker decides to shut it down.

If President Donald Trump, through Whitaker or his full-time replacement, does indeed order Mueller to shutter his investigation into Russia’s interference in the 2016 U.S. election, that would trigger a quick response from Democrats. In two months, they will wield the all-important power of subpoenaing officials.

Democrats’ first step would be to preserve evidence Mueller has collected over roughly the last year and a half so that the Trump administration doesn’t confiscate files and hide them.

Watch: The Moment Chuck Schumer Learned Jeff Sessions Was Fired

What does he know?

With their new majority, Democrats could bypass Trump’s Justice Department, which has the authority to enforce or toss out congressional subpoenas, by subpoenaing Mueller himself to learn what he knows.

“You would think Mueller would be in a cooperative mood under those circumstances,” said Kurt Bardella, a former GOP aide for the House Oversight Committee.

“Either [top House Intelligence Committee Democrat] Adam Schiff or Judiciary or Oversight or all three — I would imagine they’d do this jointly — would issue a subpoena for all the documents that Mueller had in possession at the time of his removal,” Bardella said. “It would have to be a subpoena because it’s classified information.”

Democrats could then essentially move the investigation under the jurisdiction of a congressional committee and hire Mueller, to see it through with full subpoena power. That assumes Mueller would be willing to effectively work for Democrats in a highly politicized role.

The Democrats could — and probably would — instead establish a select committee with Mueller or another hand-picked investigator as the committee’s chief counsel.

And Mueller might be able to unilaterally turn over his trove of evidence to  local law enforcement jurisdictions — the district attorney in Manhattan or the New York attorney general’s office, to name two possibilities — where alleged crimes were committed.

Politico reported in 2017 that Mueller’s team had shared evidence with the New York attorney general’s office. 

Trump appears to believe that a confrontational game of chicken with House Democrats can be a political point machine for him. That’s evident from the events of Wednesday, including the forced resignation of Attorney General Jeff Sessions, Trump’s combative press conference, and his tweets threatening political opponents with counter-investigations for conducting oversight of his administration. 

“If the Democrats think they are going to waste Taxpayer Money investigating us at the House level, then we will likewise be forced to consider investigating them for all of the leaks of Classified Information, and much else, at the Senate level,” Trump tweeted Wednesday morning. “Two can play that game!”

Senate Majority Leader Mitch McConnell is apparently on the president’s side, warning House Democrats multiple times at a press conference Wednesday not to go overboard on “presidential harassment.”

Crossing a line?

But if Trump fires Mueller, Democrats say they would have no choice but to respond with rigorous oversight.

“If you’ve triggered a constitutional crisis, you’ve triggered a constitutional crisis. And that can’t be ignored,” said Virginia Rep. Gerald E. Connolly, the second-in-line among Democrats on the House Oversight Committee.

Connolly dismissed the notion that Trump, by ousting Sessions the day after Democrats secured control of the House, is intentionally baiting them into playing up impeachment proceedings. That’s a direction  leaders of the party have so far been loath to discuss.

“Our experience with Trump is he’s more impetuous than that,” Connolly said. “There may be method to his madness, but he’s also reckless and impetuous. And he may not have thought this through at all.”

Trump and other Republicans warned ahead of the midterms that Democrats would move to impeach Trump upon winning a majority in the House, even though Democratic Speaker front-runner Nancy Pelosi of California and projected House Judiciary Chairman Jerrold Nadler have made it clear that they plan to wait for Mueller to conclude his investigation. 

But Democrats had a warning of their own for Trump: If you fire Mueller, we’re going to investigate the circumstances of that decision — you don’t want that.

By firing Mueller, Trump would potentially be laying himself a trap by opening his administration and Justice Department up to yet another investigation, this one a sweeping probe into the circumstances surrounding the decision to shut down the special counsel.

Even if Trump and his inner circle refused to cooperate, there are always whistleblowers within the government who are all too eager to tattle on higher-ups for indiscretions, Bardella said.

“No matter how these [House oversight investigations] start, once they do … it is almost impossible for the administration to control the outcome,” Bardella said.

He cited hearings into an attack in Benghazi in which a U.S. ambassador and three others died as an example of a House select committee probe that ran far afield from its original purpose after investigators discovered tangential indiscretions and avenues of inquiry. 

“Benghazi started as an investigation into embassy security,” Bardella said.

“No one at time had any idea it would lead to the discovery that Hillary Clinton had a private email server. When we asked for all the documents from Secretary Clinton and she couldn’t produce them, it begged the question, ‘Why is that?’”

Even if Trump and Sessions’ successor do allow the special counsel’s investigation to run its course, Democrats fully intend to revive and launch a number of other probes that they feel have been neglected by House GOP lawmakers who’ve proven unwilling to conduct executive branch oversight and instead sought to insulate the president from his own Justice Department’s inquiry.

“All of that tearing down of the independence of these institutions is going to end,” Schiff, the likely incoming chairman of the House Intelligence Committee, said Wednesday in an interview with MSNBC.

The California Democrat has said he’s planning to reopen the panel’s shuttered Russia investigation.

There is a list of about 70 people, organizations and companies that Democrats say the GOP failed to adequately examine.