President Donald Trump on Tuesday escalated his attacks on Democrats' impeachment efforts, referring to the inquiry as a "coup."

"As I learn more and more each day, I am coming to the conclusion that what is taking place is not an impeachment, it is a COUP," he said.

As I learn more and more each day, I am coming to the conclusion that what is taking place is not an impeachment, it is a COUP, intended to take away the Power of the.... — Donald J. Trump (@realDonaldTrump) October 1, 2019

The House last month launched a formal impeachment inquiry stemming from a July 25 phone call between Trump and the Ukrainian president as well as a related whistleblower complaint.

The tweets came hours after reports that former Ukraine special envoy Kurt Volker and former Ukraine Ambassador Marie Yovanovitch would be sitting for depositions before the House committees involved in the impeachment inquiry.

The State Department’s Inspector General also scheduled a surprise briefing for Wednesday with staffers from a group of House and Senate committees on documents related to the State Department and Ukraine, multiple Congressional sources told NBC News.

Earlier Tuesday, Trump's trade adviser Peter Navarro told Fox Business Network he thought the president was the victim "of an attempted coup d'etat."

"This is a very dangerous game that I think the Democrats could play," Navarro said.

A coup is generally defined as a sudden, violent overthrow of a government or a seizure of power.

The impeachment process, however, is set out in the U.S. constitution.

Trump has claimed to be the victim of takeover attempts before — he called former Special Counsel Robert Mueller's probe into Russian interference in the 2016 election an "attempted coup."

"They tried for a coup, it didn't work out so well. And I didn't need a gun for that one, did I?," Trump told a crowd at the National Rifle Association’s annual meeting in Indianapolis in April.

The president on Sunday also promoted a quote from a pastor who told Fox News that impeaching the president would lead to a "Civil War-like fracture in this nation."