President Donald Trump on Sunday night launched a Twitter offensive against Democrats, a whistleblower who lodged a formal complaint against him, and Rep. Adam Schiff, the chairman of the House Intelligence Committee.

In a series of tweets, Trump accused Schiff of treason and demanded to meet with his accuser.

House Speaker Nancy Pelosi announced last week that the House would launch a formal impeachment inquiry into Trump's activities — in particular, a July 25 phone call between Trump and Ukrainian President Volodymyr Zelensky.

The intelligence official who lodged the whistleblower complaint against Trump on August 12 detailed concerns that Trump pressured Ukraine to investigate former Vice President Joe Biden and his son on allegations of corruption.

Last week, the complaint was declassified, and the White House released a memo about the call that appeared to corroborate it.

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President Donald Trump used Twitter on Sunday night to lash out at Democrats, the whistleblower who lodged a formal complaint against him, and Rep. Adam Schiff, the chairman of the House Intelligence Committee.

Last week, House Speaker Nancy Pelosi announced that the House would launch a formal impeachment inquiry, in light of an intelligence official's whistleblower complaint centering on a July 25 phone call between Trump and Ukrainian President Volodymyr Zelensky.

The official lodged the complaint on August 12, two weeks after the call. The intelligence community inspector general, Michael Atkinson, deemed it "credible" and of "urgent concern" and passed it on to the acting director of national intelligence, Joseph Maguire.

The complaint, which was declassified last week, alleged that Trump pressured Ukraine to investigate former Vice President Joe Biden. The White House last week also released a memo about the call, which appeared to confirm that Trump pressed Zelensky to open an investigation into corruption allegations against Biden and his son Hunter.

Read more: Trump is facing the biggest firestorm of his presidency because his own staffers blew the whistle on him

Schiff told ABC's "This Week" on Sunday that he expected the whistleblower to testify "very soon," once security measures are in place to protect their identity.

Trump on Sunday night went off on Twitter, accusing Schiff of treason and demanding to meet with his accuser.

"Like every American, I deserve to meet my accuser, especially when this accuser, the so-called 'Whistleblower,' represented a perfect conversation with a foreign leader in a totally inaccurate and fraudulent way," Trump wrote.

"I want Schiff questioned at the highest level for Fraud & Treason," he said. "In addition, I want to meet not only my accuser, who presented SECOND & THIRD HAND INFORMATION, but also the person who illegally gave this information, which was largely incorrect, to the 'Whistleblower.' Was this person SPYING on the U.S. President? Big Consequences!"

In another tweet, Trump accused Democrats of "lying & cheating like never before in our Country's history in order to destabilize the United States of America & it's upcoming 2020 Election." He also described Democrats and the media as "Dangerous & Bad."

Trump has denied that he said anything inappropriate during his phone call with Zelensky, and he suggested on Thursday in a closed-door meeting that the whistleblower is "almost a spy."

Maguire told the House Intelligence Committee on Thursday that both the whistleblower and the inspector general "acted in good faith throughout" and "have done everything by the book and followed the law."