Transcript for Nancy Pelosi says House will go forward with Trump impeachment inquiry
And we begin tonight with the rare and historic move in Washington late today. House speaker Nancy Pelosi telling fellow Democrats to follow the facts, she was before the cameras a short time ago, saying president trump has, quote, seriously violated the constitution. Speaker Pelosi saying no one is above the law, announcing an official impeachment inquiry will now move forward. It comes after the president acknowledged he brought up Joe Biden in a phone call with the Ukrainian president, and today talking about why hundreds of thousands of dollars of aid to Ukraine was being held back. So, tonight here, what comes next? What has speaker Pelosi now set into motion after declaring the president must be held accountable? And this evening, the president calling this a witch hunt. What he says he will now release. ABC's Mary Bruce leads us off from the hill tonight. Reporter: She's resisted for months, but tonight, speaker Nancy Pelosi finally made her move. The times have found us today. I'm announcing the house of representatives is moving forward with an official impeachment inquiry. Reporter: It comes just days after the president acknowledged he had asked the president of Ukraine to investigate his political rival Joe Biden and his son, hunter. Today, the president admitted that days before the conversation, he ordered his chief of staff to halt nearly $400 million in foreign aid to Ukraine. But he insists holding that money was not an attempt to pressure the Ukrainian president. And there was never any quid pro quo. Reporter: But the president has offered shifting reasons for why he stopped those payments. Just 24 hours ago, he said he withheld the money because he wanted to get Ukraine to address corruption. Why would you give money to a country that you think is -- is corrupt? Reporter: But today, he said he withheld those hundreds of millions for a different reason. I want other countries to put up money. I think it's unfair that we put up the money. Then people called me and said, let it go and I let it go. But we paid the money. The money was paid. Reporter: There is no evidence Joe Biden or his son acted improperly with regard to Ukraine. Today, the candidate fired back at president trump. But if we allow a president to get away with shredding the United States constitution, that will last forever. Reporter: While the president was at the U.N. -- More Democrats are supporting impeachment. What is your reaction to that, sir? Reporter: Capitol hill, a flurly of activity in the past 24 hours. A wave of Democrats declaring now is the time to impeach. We cannot delay. We must not wait. Reporter: And in front of a packed crowd, Nancy Pelosi was asked if the president had committed impeachable offenses. And gave a hint of what she was about to do. And if that is the case, that the president of the united States would ask a foreign government to assist him in a political way, that would be wrong. Would it be impeachable? Reporter: Just a few hours later, Pelosi made her position crystal clear. The actions of the trump presidency revealed 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. And so let's get to Mary Bruce, live with us from the hill tonight. And Mary, speaker Pelosi has resisted calls for impeachment for months, you have reported on this, but she says the president's actions involving this phone call, holding hundreds of millions in U.S. Aid, all of this, she said, made it unavoidable today? Reporter: David, Pelosi made very clear the tipping point here was the president's admission that he talked to a foreign leader about investigating his political rival. That is what broke the dam here for Pelosi and scores of other Democrats. Tonight, at least 181 members, more than two-thirds of house Democrats, now say it is time to David? Mary Bruce leading us off.
This transcript has been automatically generated and may not be 100% accurate.