House Speaker Nancy Pelosi is expected to announce a formal impeachment inquiry into President Donald Trump on Tuesday, two sources told CNBC.
Earlier Tuesday, Pelosi said that Democrats are "ready," when asked whether she and her caucus will take steps toward Trump's impeachment.
"That's why I've said as soon as we have the facts, we're ready. Now we have the facts, we're ready … for later today," Pelosi said at The Atlantic Festival in response to a question about impeachment.
The Washington Post reported earlier Tuesday afternoon that Pelosi would announce a formal impeachment inquiry after meeting with Democratic lawmakers.
She is expected to make a statement around 5 p.m. ET, following meetings with congressional leadership and her caucus, according to NBC News.
Pelosi has until now resisted Democrats' calls for Trump's impeachment, which have grown steadily in intensity since the release of special counsel Robert Mueller's Russia report.
She has been privately weighing a possible impeachment inquiry for months — but early Tuesday morning, Pelosi's allies were convinced she would not go down that route, sources told CNBC.
Hours later, however, those same people were told that she's planning to move ahead with the inquiry, the sources said.
But more than a dozen Democrats have come out for impeachment within the past week, following bombshell reports that Trump had asked Ukraine President Volodymyr Zelensky multiple times to investigate Biden's son, Hunter Biden, during a phone call in July.
The latest converts include more moderate Democrats, some of whom represent districts that went for Trump in the 2016 presidential election, such as Rep. Abigail Spanberger of Virginia.
Sen. Dick Durbin of Illinois, the No. 2 Democrat in the Senate, also called for an impeachment inquiry Tuesday.
Biden, the Democratic front-runner in the 2020 presidential primary, will say Tuesday afternoon that if Trump does not comply with congressional inquiries, then lawmakers have no choice but to impeach him.
"The Democrats continue to weaponize politics when they should be working on behalf of their constituents, which is nothing new," Whtie House press secretary Stephanie Grisham said in a statement. "President Trump is working hard on behalf of our country here in NYC while they continue to scream the word impeachment. Nothing new here."
More than two-thirds of the 235-member House Democratic caucus now support either impeachment or launching an impeachment inquiry, according to NBC's running count. One independent representative, Michigan's Justin Amash, also favors an impeachment inquiry.
The Washington Post and other outlets reported Monday that Trump had directed his acting chief of staff, Mick Mulvaney, to withhold hundreds of millions of dollars in military assistance to Ukraine at least a week before the call with Zelensky. The timing of that move, which was criticized at the time as being opaque, has bred speculation that Trump may have used the aid as leverage to pressure Zelensky into investigating Biden.
That aid money was eventually sent earlier in September. Trump has denied that the assistance to Ukraine was mentioned in the call.
Trump, who is New York this week for the U.N. General Assembly, has acknowledged mentioning Biden in the call. Earlier Tuesday, Trump also confirmed that he delayed the funds to Ukraine, saying he did it because other countries weren't contributing enough.
In a pair of tweets Tuesday, Trump said he had authorized the release on Wednesday of the complete transcript of the call.
The call with Zelensky is reportedly the subject of a whistleblower's complaint, which is being kept from congressional review by the Department of Justice. The specific text of that complaint has not yet been publicly disclosed.
That whistleblower now wants to speak to the House Intelligence Committee, according to its chairman, Rep. Adam Schiff, D-Calif.
Lawyers for the whistleblower did not immediately respond to CNBC's questions about Schiff's tweet.
Trump and his lawyer, Rudy Giuliani, have accused Biden and his son of political corruption over then-vice president Biden's pressure on Ukraine to fire a prosecutor who reportedly oversaw a probe into the owner of a natural gas company that employed Hunter Biden.
There's no clear evidence that Biden's actions as vice president were intended to help his son, and other nations had also called for the Ukrainian prosecutor's resignation. Hunter Biden has not been accused of wrongdoing related to his work with the company, The New York Times reported.
Ahead of Pelosi's remarks Tuesday, she and House Majority Leader Steny Hoyer, D-Md., announced that the House will vote on a resolution criticizing the Trump administration's refusal to release the complaint "and the need to protect the whistleblower."
That resolution is non-binding and would not force the Trump administration to do anything.
This is a developing story. Please check back for updates.