Speaker Nancy Pelosi Nancy PelosiDemocratic senator to party: 'A little message discipline wouldn't kill us' Overnight Health Care: New wave of COVID-19 cases builds in US | Florida to lift all coronavirus restrictions on restaurants, bars | Trump stirs questions with 0 drug coupon plan Overnight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds MORE (D-Calif.) left a draft of her speech announcing a formal impeachment inquiry into President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE on a plane during a flight back to Washington, D.C., earlier this week.

Pelosi told Politico that she began writing notes for a speech endorsing an impeachment inquiry after consulting with a group of freshman Democratic lawmakers who published a Washington Post op-ed voicing support for impeachment if allegations regarding the president's interactions with his Ukrainian counterpart were true.

“I put down some notes on the plane at 10 p.m. at night but then I left it on the plane,” Pelosi told the news outlet.

Reuters, citing a source familiar with Pelosi's notes, reported that the Speaker had drafted a speech while flying from New York to Washington.

“At least she had organized it in her head,” the source said.

Pelosi's decision to announce a formal impeachment inquiry into Trump marked a significant shift for the House leader, who had up to then repeatedly resisted calls for impeachment.

Pelosi said late Tuesday that she arrived at her decision following allegations that Trump pressured the leader of Ukraine to investigate 2020 presidential candidate Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE and his son Hunter Biden over allegations of corruption.

She joined 218 House Democrats who have now publicly endorsed an impeachment inquiry into the president.

“Our republic endures because of the wisdom of our Constitution enshrined in three co-equal branches that act as checks and balances,” Pelosi said from a flag-adorned Speaker’s Balcony behind her office in the Capitol. “The president must be held accountable. No one is above the law.”

The move came amid an escalating controversy prompted by a whistleblower complaint within the intelligence community. A source familiar with the complaint told The Hill that the documents focus on Trump's interactions with Ukrainian President Volodymyr Zelensky.

Following its release, Pelosi said that the details of the conversation confirmed the need for an impeachment inquiry, adding that "it is not part of [Trump's] job to use taxpayer money to shake down other countries for the benefit of his campaign."

"Either the president does not know the weight of his words or he does not care about ethics or his constitutional responsibilities,” she said.