US House Speaker Nancy Pelosi announced on Thursday that the Democrats will begin drafting articles of impeachment against President Donald Trump.

Pelosi argued that the president’s conduct when it came to Ukraine left Democrats with “no choice but to act,” charging that Trump abused the powers of the presidency and leaving little doubt that the House will hold a vote to impeach him as early as before Christmas.

“His actions are in defiance of the vision of our founders and the oath of office that he takes to preserve, protect and defend the Constitution of the United States,” Pelosi said.

Democrats allege Trump withheld a White House meeting and military aid, sought by Ukraine in the face of Russian military aggression, to force Zelensky to order official inquiries into former vice president Joe Biden and his son Hunter Biden, as well as an unfounded theory that Kyiv conspired with Democrats to interfere in the 2016 presidential election.

There is no appetite for trying to impeach Trump on grounds of treason, the third specific act listed in the Constitution’s definition of impeachable offences, according to people familiar with the plans.

Earlier on Thursday, Trump dared Democrats to act quickly, turning his focus to the Senate where the White House has already previewed an aggressive defense strategy that could entail calling witnesses to the chamber floor.

On Tuesday, US Democrats accused President Trump of abusing power to win re-election in 2020 and said that will form the basis of any formal impeachment charges that he solicited foreign interference, undermined national security, and ordered an unprecedented campaign to obstruct Congress.

In November, Trump had described the impeachment probe against him as “witch hunt” and said he was “too busy” to watch it.

Trump administration had ordered officials not to participate in the House enquiry. But lawmakers have spent weeks hearing from current and former government witnesses, largely from the State Department, as one official after another has relayed his or her understanding of events.

After almost a month of calling for greater transparency in the enquiry, the White House changed its strategy this week by prohibiting several of its officials from even testifying behind closed doors before the lower house committees.

Late September, the impeachment inquiry, which House Speaker Nancy Pelosi initiated over a complaint by an anonymous whistleblower, is looking into White House’s alleged efforts to withhold military aid to have Ukraine investigate a Trump’s political rival, Joe Biden.

(With inputs from agency)