House Speaker Nancy Pelosi told fellow Democrats in the House on Tuesday that she supports the launch of impeachment proceedings into the president, in what represents a historic black mark for an administration not yet through its first three years in office.

The inquiry was prompted by allegations that Trump pressured Ukrainian officials to investigate former Vice President Joe Biden and his son in exchange for military aid, though Pelosi has instructed several committees to compile impeachable offenses on other fronts as well.

Only three presidents have been subjected to formal impeachment proceedings while in office, none as they were facing re-election.

“Today, I am announcing the House of Representatives moving forward with an official impeachment inquiry,” Pelosi declared after a hour-long meeting of her members. “The president must be held accountable. No one is above the law.”

Several sources said that the Speaker is not conditioning the move on impeachment on President Trump producing a whistleblower complaint that prompted questions of whether he leveraged military aid to compel a foreign government to damage a political rival. The speaker said that the Director of National Intelligence had a choice before testifying before Congress on Thursday: “He will have to choose whether to break the law or honor his duty to the Constitution.”

At the heart of Pelosi’s support for impeachment proceedings is Trump’s call with Ukrainian president Volodymyr Zelensky. Details of the call have been reported by several news outlets, came to light in the wake of the complaint from an anonymous whistleblower who has attempted to get their report before lawmakers. The Trump administration moved last week to block that complaint from reaching the House Intelligence Committee, even though such complaints require a congressional review if they are deemed urgent—which the whistleblower’s complaint was.

House Intelligence Chairman Adam Schiff (D-CA) announced on Tuesday—before Pelosi’s appearance—that his committee might see testimony from the whistleblower as soon as this week. The whistleblower is reportedly aiming to speak to members of the GOP-led Senate Intelligence Committee, which will see testimony from the acting Director of National Intelligence, Joseph Maguire, on Thursday.

Meanwhile, Trump tweeted from the United Nations General Assembly that he would release an un-redacted transcript of his phone call with Zelensky as soon as Wednesday. Speaking at The Atlantic magazine festival in D.C. earlier Tuesday, Pelosi made clear that transcripts were the beginning, not the end, of attempts to get to the bottom of the Ukraine matter and that there were other issues that would inform impeachment proceedings beyond what happened in Ukraine.

This week’s turn of events has pushed Pelosi into territory that seemed unimaginable just days ago. The longtime House Democratic leader has worked to quell the brewing impeachment movement in her caucus from the moment she took the speaker’s gavel in January. She managed to pull off that feat even as Special Counsel Robert Mueller’s report detailed possible obstruction of justice by the president and the administration stonewalled Democrats’ subpoenas for documents and testimony to learn more. That obstruction helped swelled the ranks of House Democrats who backed impeachment. But the past few days have brought the number to a near-critical mass and lawmakers said on Tuesday that there was full support for the speaker's announcement.

“I think that the most important thing that I think I would just convey to you is that unlike any other caucus meeting, there was broad consensus. I did not hear one word of dissent,” said Rep Raja Krishnamoorthi (D-IL). “And that’s the first time that I recall, that’s occurred in a discussion of the President.”

Pelosi’s reluctance to move forward—rooted in the belief that an impeachment proceeding based on these topics would backfire politically—frustrated the party’s progressive base but largely satisfied the moderates who delivered Democrats their majority in 2018.

The calculus has clearly changed, due to a string of explosive news reports detailing activity by Trump that would be far easier to work into an impeachment case than what Mueller outlined.

Indeed, those same reluctant moderates have, in the past 24 hours, come out in droves to express support for impeachment. Freshman House Democrats who flipped seats that were long held by Republicans—and that Trump won in 2016—voiced support for impeachment based on the Ukraine story, though many said they’d back impeachment if the Ukraine allegations were proven by congressional investigators. At the same time, progressive holdouts closely allied with Pelosi jumped on the impeachment train, too, signaling that they privately had the speaker’s backing.

As of Tuesday afternoon, a majority of House members were publicly supportive of impeachment.

With reporting by Jackie Kucinich