Nevertheless, she insisted.

While most fellow 2020 Democratic presidential hopefuls ducked and dived to find safe ground — and party elders solemnly warned against over-reach — Sen. Elizabeth Warren stepped boldly out into the open late Friday and called on the House to begin an impeachment process against President Donald Trump based on special counsel Robert Mueller's report.

The Massachusetts senator and 2020 Democratic presidential contender slammed Trump for having "welcomed" the help of a "hostile" foreign government and having obstructed the probe into an attack on an American election.

"To ignore a President's repeated efforts to obstruct an investigation into his own disloyal behavior would inflict great and lasting damage on this country," Warren tweeted. "The severity of this misconduct demands that elected officials in both parties set aside political considerations and do their constitutional duty. That means the House should initiate impeachment proceedings against the President of the United States."

It was a rare moment in a crowded and unsettled primary: A seized opportunity for a candidate to cut through the campaign trail cacophony and define the terms of a debate that will rage throughout the contest.

With her party torn between its impulses — to avoid the potential political death spiral of a failed impeachment even though it may be popular with the energized base and to hold Trump accountable for what Democrats see as gross abuses — Warren framed pursuing House hearings as a matter of conscience.

In other words, she sided with that base of core party supporters, defined its cause in moral terms and hollered the message from the mountaintop.

That's classic Warren. And in a period when she's focused her campaign on serious policy proposals, it is a timely reminder to progressives that they like her politics, too.

Download the NBC News app for breaking news and politics

"Not doubting her sincerity here but it's also probably a very shrewd primary move to leap out front on this," tweeted David Axelrod, who served as a top campaign and White House adviser to President Barack Obama.

A campaign official told NBC News Warren believed it was the right course of action after reading Mueller's report during a flight home from the campaign trail Thursday. Nevertheless, she will remain focused on her policy platform, not impeachment, the official said.

And yet, calling for the removal of a president — especially when so many other Democrats are reluctant to do so (shortly before Warren issued her statement, fellow senator and 2020 hopeful Amy Klobuchar said, "I think you've seen all the senators are very cautious about talking about this because we would be the jury if there was any kind of an action brought over from the House") — isn't a particularly forgettable act.

Adam Green, co-founder of the Progressive Change Campaign Committee, which has endorsed Warren, said the political left is outraged over the handling of the Mueller report by Attorney General William Barr and the response by the White House.

Warren's move could help her capitalize on that energy at a time when several of her rivals have been garnering more attention — as well as bigger fundraising hauls and higher poll numbers — in the early months of the primary campaign.

"If you think about the oxygen that is now in the room for the entire Russia-Mueller-impeachment swirl of stuff, for weeks or months, every time someone comes out publicly and agrees that we need to begin impeachment hearings, people will remember that Elizabeth Warren is the presidential candidate that got that started," Green said.

While Green noted Rep. Rashida Tlaib, D-Mich., introduced the House resolution that would be a likely vehicle for beginning impeachment hearings, Warren's status as a significant player in the primary will likely make her announcement a major marker if the House moves forward against the president.

At nearly the same time as Warren spoke out, fellow progressive Bernie Sanders, the polling leader among candidates currently in the race, waved off press questions about the Mueller report in South Carolina.

On Thursday, former Rep. Beto O'Rourke, D-Texas, who said during his Senate campaign last year against Ted Cruz that he would vote to impeach Trump, framed the question as one for Congress or the voters — rather than presidential candidates.

Asked about impeachment proceedings, O'Rourke says: "I'm gonna leave that to those members of the House who as they review those findings can make that decision. ... But ultimately at this point I believe that this is going to be decided in November 2020." https://t.co/kAEhVFeYdP — Patrick Svitek (@PatrickSvitek) April 18, 2019

Mayor Pete Buttigieg of South Bend, Indiana, said he was "pretty sure" Trump "deserves to be impeached" but deferred to Congress, while former Housing and Urban Development Secretary Julián Castro, speaking before Warren, said it would be "perfectly reasonable" for lawmakers to launch impeachment proceedings. "This president should be held accountable," Castro said on MSNBC.

Sen. Kamala Harris, D-Calif., said on MSNBC's "All In with Chris Hayes" on Thursday that she wants to hear what Mueller has to say about his report before passing judgment on whether impeachment proceedings should begin — similar to the position of her fellow Californian, House Speaker Nancy Pelosi, perhaps the most important player in any impeachment drama.

The reticence of some Warren's rivals suggests her decision to walk point on the left flank of the impeachment front carries some risk, even if it's a quick path to rally support from liberals.

It will not only put her squarely back in Trump's field of vision, but it also will expose her to friendly political fire from Democrats who believe pursuing his ouster is the surest way to ensure his re-election.

Still, Warren, often cited as the heir to Edward M. Kennedy as the liberal lion of the Senate, has shown that her brand can be most compelling when a healthy dose of politics is mixed in with her substance.

That's what happened when GOP senators cited the chamber's rules to take away Warren's speaking privileges during a 2017 debate over Trump's nomination of Jeff Sessions to be attorney general. Warren had read from a letter criticizing Sessions that had been written by Coretta Scott King in 1986.

Since Sessions was a member of the Senate at the time of the nomination fight, Warren was told she couldn't malign him under the rules. The Senate voted to prevent her from speaking again on Sessions' nomination.

"She was warned. She was given an explanation," Senate Majority Leader Mitch McConnell, R-Ky., said afterward. "Nevertheless, she persisted."

Progressives quickly adopted McConnell's disparaging phrase as a symbol for strong women. It was even condensed to "She Persisted" for the title of a bestselling book by Chelsea Clinton.

It remains to be seen whether Warren's impeachment call will give her a major boost. But there aren't many opportunities to stand out from the crowd, and she took this one without hesitation.