President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE lashed out at Democrats the morning after Speaker Nancy Pelosi Nancy PelosiDemocratic senator to party: 'A little message discipline wouldn't kill us' Overnight Health Care: New wave of COVID-19 cases builds in US | Florida to lift all coronavirus restrictions on restaurants, bars | Trump stirs questions with 0 drug coupon plan Overnight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds MORE (D-Calif.) announced a formal impeachment inquiry.

"There has been no President in the history of our Country who has been treated so badly as I have. The Democrats are frozen with hatred and fear," he tweeted on Wednesday.

"They get nothing done," he added. "This should never be allowed to happen to another President. Witch Hunt!"

There has been no President in the history of our Country who has been treated so badly as I have. The Democrats are frozen with hatred and fear. They get nothing done. This should never be allowed to happen to another President. Witch Hunt! — Donald J. Trump (@realDonaldTrump) September 25, 2019

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“Our republic endures because of the wisdom of our Constitution enshrined in three coequal branches that act as checks and balances,” Pelosi said late Tuesday in the Capitol. “The president must be held accountable. No one is above the law.”

Pelosi, who had rejected moving forward with impeachment for months, made the announcement after Trump admitted that he had spoken to Ukraine’s president about looking into former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE, a leading candidate for the Democratic presidential nomination, just weeks after withholding military aid to that country.

Trump has denied any wrongdoing.

Pelosi's announcement followed a wave of support for impeachment from House Democrats on Tuesday in response to the Ukraine revelations. More than three-quarters of the House Democratic Caucus now support the start of an impeachment inquiry.

Trump also slammed Democrats minutes after Pelosi announced the impeachment proceeding.

“Such an important day at the United Nations, so much work and so much success, and the Democrats purposely had to ruin and demean it with more breaking news Witch Hunt garbage. So bad for our Country,” he tweeted Tuesday night.

The president has confirmed he brought up Biden during a July call to Ukrainian President Volodymyr Zelensky but denied pressing the leader to look into the Democratic front-runner.

Trump has also said he held up aid because he wanted other countries to contribute more funds to help Ukraine.

— This report was updated at 7:48 a.m.