WASHINGTON — In a historic move, the U.S. House of Representatives will commence an official impeachment inquiry after a cascade of Democrats on Tuesday called for the start of proceedings that could lead to the removal of President Donald J. Trump.

At the end of a day in which a flood of House Democrats, including U.S. Reps. Antonio Delgado and Paul Tonko, called for immediate movement toward impeachment, House Speaker Nancy Pelosi, D-Calif., announced the beginning of formal House action.

In a statement that cited the Founding Fathers numerous times, Pelosi said the president "must be held accountable — no one is above the law."

The president, at Trump Tower in midtown Manhattan after attending a United Nations gathering, lashed out in a series of Tweets.

"Such an important day at the United Nations, so much work and so much success, and the Democrats purposely had to ruin and demean it with more breaking news Witch Hunt garbage," he wrote. "So bad for our Country!"

Meanwhile, in another major symbolic step, the GOP-led Senate unanimously passed a resolution put forward by Senate Minority Leader Charles E. Schumer calling on the Trump administration to immediately provide the House and Senate intelligence committees with a copy of a whistleblower complaint involving Trump.

The extraordinary steps from Congress are in response to allegations that Trump tried to persuade the president of Ukraine, Volodymyr Zelensky, to investigate one of his 2020 political rivals, former Vice President Joe Biden. Trump has admitted to discussing Biden with Zelensky, but insists the conversation was appropriate.

The White House said it would release a declassified copy of a transcript of his call with Zelensky, likely on Wednesday.

But lawmakers of both parties want to see the whistleblower complaint, which allegedly describes their conversations.

The complaint will be the subject of a key hearing by the House Intelligence Committee Thursday. Rep. Elise Stefanik, R-Schulyerville, sits on the committee and previously asked for the release of the whistleblower complaint.

"I strongly believe in the importance of transparency," Stefanik said Tuesday night. "I support the president's decision to release the entire transcript of his call with the Ukrainian president to the American public. I do not support impeachment of the president."

Six House committees, including the Intelligence Committee, will now investigate the president's actions with Ukraine.

The impeachment inquiry is expected to increase the partisan divide in Washington, and possibly across the nation. It will be central to Democrats' 2020 campaigns for the presidency.

And whether or not the impeachment effort is successful, it is certain to influence Trump's legacy. Only three presidents have been subject to impeachment proceedings. Two, Andrew Johnson and Bill Clinton, were impeached and Richard M. Nixon resigned to avoid impeachment.

Delgado, a Democrat from Rhinebeck who had previously been resistant to impeachment, said in a statement early Tuesday morning that he supported moving ahead with an inquiry because Trump "placed his personal interests above the national security of our nation."

"The president has admitted to soliciting the Ukrainian president to investigate a political rival. This, by itself, is an impeachable offense," Delgado said.

Delgado said he was deeply troubled by allegations that millions of dollars of military aid to Ukraine was briefly withheld from the country, possibly in connection with the Trump campaign's request that Ukraine investigate Biden's son, Hunter Biden.

"Having taken an oath of office before God and my fellow citizens to support and defend the Constitution of the United States, I can only conclude that Congress move forward with articles of impeachment," Delgado said.

Delgado's decision drew immediate criticism from national Republican groups who are widely attacking the wave of Democrats now urging impeachment. Delgado represents a district that is now rated a political tossup.

"In a district President Trump won by more than six points, Antonio Delgado's decision to pursue impeachment will be a political death sentence," said Michael McAdams, a spokesman for the National Republican Congressional Committee.

Tonko said recent news about Trump's contacts with Ukraine convinced him, like Delgado, that articles of impeachment are needed now.

"I called for an impeachment inquiry in June of this year after a careful review of (Special Counsel) Robert Mueller's report on 2016 election interference," Tonko said. "With the evidence now before us, and in service of my sworn oath to support and defend our Constitution, I see no alternative but to call for the House to file articles of impeachment immediately. And I will vote yes."

Both Tonko and Delgado's statements are among the strongest calls for House action against the impeachment in the House Democratic Caucus. Most Democrats said Tuesday they supported an inquiry, but did not float the idea of filing articles of impeachment.

U.S. Sen. Kirsten Gillibrand, D-N.Y., has her name on the short list of Senate Democrats publicly backing impeachment. She argued in favor of impeachment when she was a presidential candidate.

"I'm deeply concerned," Gillibrand told reporters Tuesday. "It's a very serious allegation. I support the House starting inquiry into this issue. We need (the) transcript (of Trump's call) and the whistleblower report, and we need the whistleblower to testify."

Trump's team has alleged that during a visit to Ukraine in 2016, Joe Biden pressured government officials there to fire a top prosecutor or the U.S. would withhold $1 billion in aid. Biden has acknowledged that account, but said it was because the prosecutor had failed to investigate widespread corruption in Ukraine.

Trump contends, without providing evidence, that Biden wanted the prosecutor fired so that he would not investigate Hunter Biden, who at the time was being paid tens of thousands of dollars per month to sit on the board of Ukraine's largest private gas company.

By attacking the president's actions toward Ukraine, Delgado joined other swing-district House Democrats who came out in favor of impeachment or an impeachment probe on Monday and Tuesday. Delgado won the office by defeating Republican U.S. Rep. John Faso in 2018.

The Congressional Leadership Fund, an influential GOP super PAC, slammed Delgado for supporting impeachment Tuesday.

"Antonio Delgado made it perfectly clear his loyalties lie with impeachment-obsessed socialists who will stop at nothing to remove President Trump from office, no matter the cost," said CLF Spokesman Calvin Moore. "Congressman Delgado's decision to back impeachment will be seared into the mind of every voter as a reminder that his irrational hatred of President Trump took priority over the will of the constituents who elected him to office in the first place."

Dan Freedman contributed to this report.