How the tide turned on a day that led to an impeachment inquiry Events Tuesday included a moment of unity in the Senate, Pelosi's announcement.

In a historic move, Speaker Nancy Pelosi announced on Tuesday that House Democrats were moving forward with an official impeachment inquiry into President Donald Trump.

"The actions of the Trump presidency revealed the dishonorable fact of the president's betrayal of his oath of office, betrayal of our national security, and betrayal of the integrity of our elections," Pelosi said. "Therefore, today I'm announcing the House of Representatives is moving forward with an official impeachment inquiry."

"The actions taken to date by the president have seriously violated the Constitution," Pelosi said. "The president must be held accountable."

Trump tweeted as soon as Pelosi finished, saying, "They never even saw the transcript of the call," referring to the phone conversation he had July 25 with Ukraine's president that is the focus of the latest impeachment controversy.

Just hours earlier, Trump promised to release an unredacted transcript of his phone call with Ukraine's president in July that has triggered a new Democratic push for impeachment.

Trump tweeted that the transcript, which he said would be made public Wednesday, would show that it was "a totally appropriate call."

"NO quid pro quo!" he said.

The fast-moving developments came amid new questions about whether Trump had made millions in military aid to Ukraine contingent on Ukraine's President Volodymyr Zelensky agreeing to investigate former Vice President Joe Biden and his son, Hunter.

Trump, who had said previously he was concerned about sending aid to Ukraine because of corruption he alleged there, gave a new explanation Tuesday, saying he had ordered the aid frozen -- before the call -- because he was unhappy with how much European countries were contributing to Ukraine.

In her formal announcement late Tuesday afternoon, Pelosi said the Trump administration blocking the whistleblower complaint from being sent to Congress was a "violation of the law" and said Trump calling on a foreign leader to interfere in a U.S. election was "a breach of his constitutional responsibilities."

Tuesday evening, two sources close to the president told ABC News that the White House is considering releasing the complaint filed by the whistleblower. The complaint, which is classified, is undergoing a declassification process, according to sources familiar with the matter.

The Democratic chairman of the House Intelligence Committee tweeted earlier in the day that the whistleblower who filed a formal complaint about Trump's call wanted to talk to his committee.

Over the past 24 hours a rapid succession of Democrats embracing impeachment has pushed Pelosi and her caucus to go forward on the matter.

The Pelosi announcement was scheduled to follow a meeting of all Democrats Tuesday afternoon with at least 166 Democrats -- more than two-thirds of the caucus - now publicly supporting impeaching President Donald Trump.

At the same time, House Democrats were drafting a resolution to pressure the Director of National Intelligence to release a whistleblower complaint to Congress. The measure will be on the floor for consideration on Wednesday, according to a senior Democratic leadership aide.

Tuesday evening, two sources close to the president told ABC News that the White House is considering releasing the complaint filed by the whistleblower. The complaint, which is classified, is undergoing a declassification process, according to sources familiar with the matter.

During a live interview at The Atlantic Festival Tuesday afternoon, Pelosi said, "This isn't about politics. If we have to honor our oath of office to support and defend the Constitution of the United States, from all enemies, foreign and domestic, that's what we're have to do.

"We have to have the facts. That's why I've said, soon as we have the facts, we're ready. Now we have the facts. We're ready. For later today. But -- but so this isn't about politics," she said.

Biden, on the campaign trail in Wilmington, Delaware, said, "If the president does not comply such a request of the Congress, if he continues to obstruct Congress and flaunt the law, Donald Trump will leave Congress in my view no choice but to initiate impeachment."

Before meeting with all House Democrats, Pelosi huddled Tuesday afternoon with her leadership team, the chairmen of six committees investigating the president and held a special caucus meeting to discuss impeachment.

In her subsequent announcement, Pelosi said all the House committees looking into alleged Trump wrongdoing would continue their work. "I'm directing our six committees to proceed with their investigations under that umbrella of an impeachment inquiry," referring to the official impeachment probe she announced. A source involved in the process told ABC News the House Judiciary Committee looking into whether Trump committed obstruction of justice would remain the main investigation.

Arriving at the Capitol Tuesday morning, Pelosi ignored a question asking whether it is time to impeach the president now that more than 150 Democrats are pressing for impeachment.

Seven freshmen Democrats, all veterans of the military, defense and intelligence agencies, wrote an op-ed in the Washington Post Monday evening calling allegations that the president pressured Ukraine to investigate Democratic presidential frontrunner Joe Biden, "a direct violation of our national security."

At the United Nations Tuesday, Trump insisted he had done nothing improper and called the new impeachment talk "ridiculous and a "witch hunt."

"If these allegations are true, we believe these actions represent an impeachable offense," Reps. Gil Cisneros, Jason Crow, Chrissy Houlahan, Mikie Sherrill, Elissa Slotkin, Abigail Spanberger, and Elaine Luria," wrote collectively. "We do not arrive at this conclusion lightly, and we call on our colleagues in Congress to consider the use of all congressional authorities available to us, including the power of "inherent contempt" and impeachment hearings, to address these new allegations, find the truth and protect our national security."

Amid the whistleblower complaint, some of Pelosi’s closest allies have also recently cut off their patience regarding impeachment, perhaps affording Pelosi with political cover and ending the prolonged defense of slow-walk the process through a thorough, methodical investigation.

Connecticut Democratic Rep. Rosa DeLauro called the complaint a "matter of grave urgency."

"As with many of my colleagues, I have been reluctant to call for an impeachment inquiry because it would further divide the country, be perceived as overturning the 2016 election, and go to the United States Senate where Republicans would acquit President Trump regardless of the evidence. But these actions regarding the 2020 election are a turning point," DeLauro wrote in a statement. "An impeachment inquiry may be the only recourse Congress has if the President is enlisting foreign assistance in the 2020 election. Congress must meet this pivotal moment in our nation’s history with decisive action."

Senate Majority Leader Mitch McConnell, reacting to Pelosi, said, "This rush to judgment comes just a few hours after President Trump offered to release the details of his phone conversation with President Zelensky."

"It comes despite the fact that committee-level proceedings are already underway to address the whistleblower allegation through a fair, bipartisan, and regular process," he said in a statement.

House Minority Leader Kevin McCarthy accused Democrats of trying to overturn the results of the 2016 election by pursuing impeachment, and of going after Trump at the expense of legislating.

"Our job here is a serious job -- our job is to focus on the American public. Our job is to make tomorrow better than today, Our job is to legislate, not to continue to investigate something in the back when you cannot find any reason to impeach this president," he said, without commenting on the substance of Democrats' concerns about Trump's actions. "This election is over. I realize 2016 did not turn out how Speaker Pelosi wanted it to happen, but she cannot change the laws of this Congress. She cannot unilaterally decide on an impeachment inquiry."

In a rare moment of unity, the entire U.S. Senate Tuesday evening unanimously passed a non-binding resolution calling on the Trump administration to release the secret whistleblower complaint to the House and Senate Intelligence committees.

McConnell did not try to block the measure and it meant that every Senate Republican -- along with every Democrat -- voted that the whistleblower complaint should be turned over to Congress -- not just the phone call transcript.

ABC News' Trish Turner, Liz Alesse, Mariam Khan, Katherine Faulders and John Santucci contributed to this report