Two hundred and eighteen House Democrats — almost the entire 235-member caucus — now support some type of impeachment action in light of President Donald Trump's burgeoning Ukraine scandal.

The fast-expanding list includes at least 82 lawmakers who have come out in favor of action since reports last week that the president pushed Ukraine to investigate the Biden family. In addition to the Democrats, Rep. Justin Amash, a Michigan independent, also favors an impeachment investigation.

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Some on this list have called for an impeachment inquiry or hearings, some believe the House Judiciary Committee is already undertaking an inquiry and are supportive of that investigation, while others have gone further and called for drafting articles of impeachment. Lawmakers are using different terms when they talk about the issue.

With pressure growing within her caucus, House Speaker Nancy Pelosi, D-Calif., on Tuesday night announced a formal impeachment inquiry into the president's actions, which she said "seriously violated the Constitution" and "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 made the announcement after meeting with the Democratic leadership, key committee chairmen, and the rest of the caucus earlier in the afternoon.

Trump responded on Twitter within minutes, calling the announcement “Witch Hunt garbage” and "presidential harassment!" The president earlier told reporters that an impeachment inquiry would help him in the 2020 election but would harm the country.

The recent impeachment drive follows days of revelations surrounding Trump's apparent push to have the Ukrainian government investigate former Vice President Joe Biden and his son Hunter, who had business dealings in the country. NBC News confirmed that Trump instructed his chief of staff to place a hold on about $400 million in military aid for Ukraine in the days before a late July phone call with Ukrainian President Volodymyr Zelensky, as reported by The Washington Post and other media outlets Monday.

In a Washington Post op-ed article Monday night, seven freshman House Democrats called for impeachment hearings in response to the controversy, which three sources told NBC News might give Pelosi "cover" to back a formal impeachment proceeding against the president.

"This is major. It seems to me like it's an inflection point," one source said.

In the op-ed article, Reps. Gil Cisneros of California; Jason Crow of Colorado; Chrissy Houlahan of Pennsylvania; Mikie Sherrill of New Jersey; Elaine Luria and Abigail Spanberger, both of Virginia; and Elissa Slotkin of Michigan said their experiences in the military, defense and U.S. intelligence agencies helped shape their decision.

"These allegations are stunning, both in the national security threat they pose and the potential corruption they represent," they wrote.

Speaking with MSNBC's "Morning Joe" on Tuesday, Spanberger and Slotkin expanded upon their op-ed, saying the Ukraine allegations are a threat to U.S. democracy.

"And, by the way, I mean, people don't remember it, but there's a hot war going on in eastern Ukraine," Slotkin said. "So you start holding back security assistance, that's a real lever to use with people. But the very basic idea of getting foreign help to influence American political process, that is beyond the pale."

Other signs of a shift in approach on the impeachment question became apparent Tuesday. Speaking on the House floor, Rep. John Lewis, D-Ga., a close Pelosi ally, said that he is “deeply concerned about the future of our democracy” and that people approach him everywhere saying that they believe “our nation is descending into darkness.”

“I share their concerns for the future of our country,” he said. "I believe, I truly believe the time to begin impeachment proceedings against this President has come. To delay or to do otherwise would betray the foundation our democracy."

A senior aide to a House Democrat told NBC News on Tuesday morning that 20 to 30 or more Democrats could announce support for impeachment action through the day.

"I think we may have critical mass by the end of the week, assuming the administration continues to refuse on the whistleblower docs," the source said, citing the whistleblower complaint that sparked the wave of scrutiny regarding the president and Ukraine.

Senate Democratic Whip Dick Durbin of Illinois also joined the calls for beginning an impeachment inquiry, saying Tuesday, “I think this may be the straw that broke the camel’s back."

“There’s so much cumulative evidence here, and many of us have wondered if this would ever see the light of day in an impeachment inquiry," Durbin added. "But I think now we have to move forward.”

Trump defends his actions on Ukraine

In response to the outcry over his call with Zelensky and the timing of the delay in Ukraine aid, Trump announced Tuesday that he would release "the complete, fully declassified and unredacted transcript" of his conversation with the Ukrainian president.

"You will see it was a very friendly and totally appropriate call," Trump tweeted. "No pressure and, unlike Joe Biden and his son, NO quid pro quo! This is nothing more than a continuation of the Greatest and most Destructive Witch Hunt of all time!"

....You will see it was a very friendly and totally appropriate call. No pressure and, unlike Joe Biden and his son, NO quid pro quo! This is nothing more than a continuation of the Greatest and most Destructive Witch Hunt of all time! — Donald J. Trump (@realDonaldTrump) September 24, 2019

Speaking to reporters at the United Nations earlier Tuesday, Trump called the ratcheting up of impeachment talk a "ridiculous witch hunt" and insisted his call with Zelensky "was perfect."

The president claimed the only way Democrats could defeat him in 2020 is through impeachment, saying "this has never happened to a president before" and "this is nonsense."

Asked about the hold on military aid, Trump said he wants other countries in Europe to pay for Ukraine's aid as well. But, he said he released the hold when "other people" called him and said, "'Oh let it go.'"

Trump has already admitted to talking about Biden with Zelensky and, in discussing that conversation with reporters on Monday, tied the military aide to the country's probing of corruption.

"We want to make sure that country is honest. It's very important to talk about corruption," Trump said Monday. "If you don't talk about corruption, why would you give money to a country that you think is corrupt?"

Later in the day, Trump denied any quid pro quo where he pledged to give Ukraine the money in exchange for further probing of the Bidens.

"I put no pressure on them whatsoever," he said. "I could have. I think it would probably, possibly have been OK if I did. But I didn't. I didn't put any pressure on them whatsoever."

The Trump-Zelensky discussion came under sharp scrutiny following the whistleblower complaint by a member of the U.S. intelligence community that media reports said was tied to the call between the two leaders. The administration is refusing to turn that complaint over to Congress.

In a letter to colleagues on Sunday, Pelosi threatened a "new stage of investigation" if the Trump administration and acting Director of National Intelligence Joseph Maguire fail to provide the whistleblower complaint when Maguire testifies in front of the House Intelligence Committee on Thursday. She said Tuesday that the House would vote a resolution on Wednesday expressing disapproval of the administration’s effort to block the release of the whistleblower's complaint.

Maguire and the national intelligence inspector general, Michael Atkinson, are also set to appear before the Senate Intelligence Committee behind closed doors Thursday afternoon.

Biden, who like Pelosi had been hesitant to call for impeachment proceedings against the president, said Tuesday that he would support doing so if Trump fails to comply with congressional investigators.

“If the president does not comply with such a request from the Congress, if he continues to obstruct Congress and flout the law, Donald Trump will leave Congress, in my view, no choice but to initiate impeachment," Biden said during brief remarks at the Hotel Du Pont in Wilmington, Delaware. "That would be a tragedy, but a tragedy of his own making.”

On Saturday, Ukrainian Foreign Minister Vadym Prystaiko said he didn't think Trump pressured Zelensky during the phone call. Trump and Zelensky were set to meet face to face this week on the sidelines of the United Nations General Assembly session in New York.

Trump and his personal attorney Rudy Giuliani have engaged in a monthslong effort to have Ukraine probe the Bidens — an effort aided by the State Department. It centers on the former vice president's 2016 call, widely backed by the international community, for Ukraine to crack down on corruption. That included a call to remove a Ukrainian prosecutor, Viktor Shokin, who was seen as ineffective and was later removed by the country's Parliament. One of the cases that Shokin was investigating involved Burisma Holdings, a natural gas company, whose board at the time included Biden's son.

Earlier this year, Bloomberg News, citing documents and an interview with a former Ukrainian official, reported the Burisma investigation had been dormant for more than a year by the time Biden called for the crackdown on corruption. The then-Ukrainian prosecutor general told the news agency he found no evidence of wrongdoing by Biden and his son. And PolitiFact reported it found no evidence to "support the idea that Joe Biden advocated with his son's interests in mind."