Pelosi made the announcement following a meeting of the House Democratic Caucus at the Capitol, saying that "the president must be held accountable" for what she called the "betrayal of his oath of office, betrayal of our national security, and the betrayal of the integrity of our elections."
The only Democratic hopeful to explicitly come out against impeachment was Rep. Tulsi Gabbard, D-Hawaii. Speaking on Fox Business' “Kennedy” on Tuesday night Gabbard said she thinks impeachment would be very "divisive" for a country that is already divided.
“Donald Trump has abused his power, obstructed justice, and violated his oath of office. He puts his political interests over our national interest,” tweeted Sen. Kamala Harris, D-Calif. “I agree with @SpeakerPelosi— no one is above the law. He must be impeached.”
Sen. Cory Booker, D-N.J., who first called for impeachment proceedings to begin in May after Special Counsel Robert Mueller spoke publicly about the findings of his Russia investigation, tweeted on Tuesday evening, “In 2016, Trump welcomed foreign adversaries to meddle in our democracy for his own gain. Now he appears to be using the same playbook to remain in power."
Mueller’s probe was intended to examine Russian election interference and whether President Trump's campaign colluded with Russian officials during the 2016 election. In the report, Mueller said he could not exonerate the president on obstruction of justice but that investigators did not find sufficient evidence to establish charges of criminal conspiracy between Russia and the Trump campaign.
Booker added, "I applaud Speaker Pelosi's announcement of an impeachment inquiry—it’s our one remaining path to ensuring justice is served.”
Pelosi specifically charged that the Trump administration had violated the law by not turning over an intelligence community whistleblower's complaint concerning a July phone call with Ukrainian President Volodymyr Zelensky. Citing testimony that the director of national intelligence is blocking the release of that complaint, she said: "This is a violation of law. The law is unequivocal."
Trump allegedly pushed Zelensky to investigate former Vice President Joe Biden and his son Hunter. The president vowed earlier Tuesday to release a "complete" transcript of his call with Zelensky on Wednesday, though it's unlikely to settle the issue in Congress.
Joe Biden has acknowledged that, when he was vice president, he successfully pressured Ukraine to fire its top prosecutor, Viktor Shokin, while Shokin was investigating the natural gas firm Burisma Holdings — where Hunter Biden was on the board.
"This week, the president has admitted to asking the president of Ukraine to take actions which would benefit him politically," Pelosi said Tuesday. "Therefore, today, I'm announcing the House of Representatives is moving forward with an official impeachment inquiry. I'm directing our six committees to proceed with their investigations under that umbrella.”
Following Pelosi’s announcement, Biden tweeted, “Pressuring the leader of another nation to investigate a political opponent — to help win an election — is not the conduct of an American President.”
Earlier Tuesday, Biden called Trump’s alleged actions “an abuse of power.”
“They undermine our national security,” Biden tweeted. “They violate the oath of office. If we allow a President to get away with shredding the United States Constitution — that will last forever.”
In remarks to reporters at the United Nations on Monday, Trump denied linking the Ukraine aid money to an investigation of the Bidens.
“No, I didn’t — I didn’t do it,” Trump said. But, he also repeatedly called the Bidens' actions in Ukraine a “disgrace,” acknowledged that Biden had come up during the call and added: "It's very important to talk about corruption. ... Why would you give money to a country that you think is corrupt?"
Sen. Bernie Sanders, I-Vt., did not immediately release a statement, but sent out a somewhat-cryptic tweet Tuesday night, writing only: "Billionaires should not be able to control our political system."
During a press conference earlier on Tuesday Sanders said, “If you're going to go forward with impeachment. You're going to have grounds to do it. I happen to believe they're authorized to do it, but you got to lay it out.”
In a statement, former Texas rep. Beto O’Rourke said he is “grateful to Speaker Pelosi for opening an impeachment inquiry into President Trump” and called her announcement “a defining moment for our country.”
“For more than two years, even as I was running for Senate in Texas, I have been clear that I support impeachment,” O’Rourke said. “We all must come to terms with what we face: a lawless president who has obstructed justice and undermined our democracy by inviting a foreign power to intervene in 2016, and who is doing it again in 2020.”
Entrepreneur Andrew Yang tweeted on Tuesday, “Given the President’s latest actions I think impeachment is the right path forward.”
Yang added: “Asking foreign leaders for political help in return for aid and then suppressing your own agency’s inquiry is egregious. There have to be limits and Congress is right to act.”
In a follow-up tweet, Yang wrote, “A reminder that successful impeachment requires a majority vote in the House and then two-thirds in the Senate. Given that there are 53 Republican Senators one would need 20 of them to support impeachment to be successful. That is highly unlikely unless there is some huge shift.”
He added that he still agrees that moving forward “is for the best,” saying it will allow for a more thorough investigation “that may unearth new details.”
Sen. Amy Klobuchar, D-Minn., tweeted simply, “The House did the right thing.”
Former Maryland Congressman John Delaney released a statement following the announcement saying he agreed with Pelosi’s decision to move forward with an official impeachment inquiry, adding that “she deserves our support.”
"The President’s behavior, combined with the administration’s refusal to cooperate, leaves her no other choice," Delaney added. "Our nation can only be as strong as the rules that govern it.”
Sen. Elizabeth Warren, D-Mass., called Pelosi's announcement "an overdue but important step.”
"Now the impeachment inquiry must move forward with the efficiency and seriousness this crisis demands," she said. "The House needs to vote on articles of impeachment—and when it comes to the Senate, I will do what the Constitution requires.”
Billionaire hedge fund manager Tom Steyer said he applauded Pelosi and Democrats in Congress who are calling for an investigation into Trump’s alleged criminal behavior.
“Removing Trump from office has always been about doing what’s right, not what’s politically convenient,” Steyer said. “We built a nationwide movement to impeach a lawless president and defend our democracy. This is just the beginning.”
Earlier this month, Steyer told Fox News' Bret Baier during an interview on “Special Report” that he thinks President Trump is “the most corrupt president in American history” and that he has “more than met the criteria for impeachment.”
Pete Buttigieg, the mayor of South Bend, Ind., did not react on social media, but in an interview on CNN on Tuesday night said the announcement is “a moment of truth for the country,” adding that “sooner or later it had to come.”
He went on to say that the announcement is also “a moment of truth for the Republican Party."
A total of 172 House Democrats have now signaled support for an impeachment inquiry. A simple majority of House members present and voting would be required to impeach the president. A highly unlikely two-thirds vote in the GOP-controlled Senate would be needed to convict and remove Trump from office.
Vice President Mike Pence would then take office in that scenario and become the 46th President of the United States.
Fox News’ Gregg Re contributed to this report.