WASHINGTON — Special counsel Robert Mueller may be the real change agent in Washington.

In the sober, restrained tones of a prep school dean, the veteran prosecutor went live on national television Wednesday to contradict President Donald Trump's mantra of "total exoneration" in the Russia probe and to tell the country that the responsibility of holding Trump accountable for possible obstruction of justice lays at the feet of Congress because the Department of Justice won't do it.

"After that investigation, if we had confidence that the president clearly did not commit a crime, we would have said that," Mueller explained at a Justice Department press conference at which he announced he was dissolving his office and resigning. "We did not, however, make a determination as to whether the president did commit a crime."

Now if Trump claims Mueller concluded there was "no obstruction," there is video of Mueller saying that's not what he determined.

Contrary to the suggestions of Attorney General William Barr, Mueller said he didn't pursue such a finding because the Justice Department has a regulation barring the indictment of a sitting president and "the Constitution requires a process other than the criminal justice system to formally accuse a sitting president of wrongdoing" — impeachment and removal from office.

Those words may be enough to kick-start an impeachment process against the president — one that House Democrats have been slowly inching toward even as they weigh the risks of a public backlash and the fact that the Senate would not oust Trump unless at least 20 Republicans voted to do so.

"The Congress holds sacred its constitutional responsibility to investigate and hold the president accountable for his abuse of power," House Speaker Nancy Pelosi, D-Calif., said in a statement.

At the very least, Mueller's remarks are turning up the pressure on House Democratic leaders from outside their caucus. Several Democratic presidential candidates, including California Sen. Kamala Harris, New Jersey Sen. Cory Booker and former Texas Rep. Beto O'Rourke, called for the impeachment process to move forward.

"The bottom line is we have got to now let the process start its course around Congress acting on what we know is essentially indictable evidence and information," Harris said, adding that she understood the special counsel's remarks to mean that without the DOJ's prohibition, an indictment would have been returned against Trump.

Booker said Congress now has a "legal and moral obligation" to begin impeachment proceedings.

Michigan Rep. Justin Amash, the only House Republican to back an impeachment inquiry so far, took to social media to announce "the ball's in our court, Congress."

There was movement in the House Democratic ranks, too.

After watching Mueller on Wednesday, Rep. Bill Pascrell, D-N.J. — who had until recently cautioned fellow Democrats against jumping into impeachment — added his name to the list of House members, now totaling more than 40, who have called for the House Judiciary Committee to launch a formal inquiry.

And Rep. Betty McCollum, D-Minn., said on Twitter that Democrats should draft articles of impeachment "as soon as possible."

Mueller's statement on camera — a medium that the reality-TV star president full well understands as more powerful and more permanent than last month's 448-page report — was damaging enough to Trump's position that the president immediately began backing down from it on Twitter.

"Nothing changes from the Mueller Report," Trump wrote. "There was insufficient evidence and therefore, in our Country, a person is innocent. The case is closed! Thank you."

Trump's right that Mueller's statement didn't depart from his report: The special counsel tried to relieve himself of the burden of appearing at an open congressional hearing by saying he would only testify to matters within the four corners of what he wrote.

But "insufficient evidence," which is the term Mueller used to describe his findings on whether Trump engaged in a conspiracy with Russia, is a far cry from the "total exoneration" the president has claimed from the report ever since Barr released a homespun summary of its findings more than two months ago.

Trump didn't bother to address the fact that Mueller told the public he would have said if he thought it was clear the president had not committed a crime.

White House press secretary Sarah Sanders took a stab at that.

"The report was clear — there was no collusion, no conspiracy — and the Department of Justice confirmed there was no obstruction," she said. But it was Barr, not Mueller, who decided not to go forward with a prosecution on obstruction.

As Mueller noted Wednesday, the Justice Department has long held that the only legal recourse against a sitting president is impeachment. And Mueller's language about the collusion question — "insufficient evidence" — is both more technical and more precise than the formulation that he found "no conspiracy" and "no collusion."

Mueller did not say whether he believed that the conspiracy part of his investigation was hamstrung by insufficient cooperation or potential obstruction of justice. But he did note why the mission he was assigned included looking into interference in the investigation itself.

"It was critical for us to obtain full and accurate information from every person we questioned," he said. "When a subject of an investigation obstructs that investigation or lies to investigators, it strikes at the core of the government’s effort to find the truth and hold wrongdoers accountable."

Not long after Mueller finished speaking, Republicans and Democrats retreated to their trenches to fire rhetorical volleys. Republicans shouted "case closed" and "move on." Democrats used Mueller's words — the too-long, didn't-read version of his report — to freshen calls for impeachment.

Of course, after a two-year investigation, these were familiar positions.

But there was something markedly different about the atmosphere in Washington on Wednesday. It was more charged, more combustible. For the first time — and perhaps the last time — Mueller spoke publicly and firmly, if in limited fashion, about what his investigation meant.

And, for the trained ear, it was unmistakable.

"He was virtually announcing 'Congress, do your job,'" NBC News legal analyst and former federal prosecutor Glenn Kirschner said on MSNBC.

That might make him the catalyst for a Democratic caucus that has been deeply ambivalent about the politics of impeaching the president.