President Donald Trump on Sunday night launched an attack against Democrats over the impeachment inquiry against him.

In two tweets Sunday, Trump suggested that House Speaker Nancy Pelosi and Rep. Adam Schiff, the chairman of the House Intelligence Committee, were guilty of treason.

Pelosi announced last month that the House would launch a formal impeachment inquiry into Trump's activities — in particular, the July 25 phone call between Trump and Ukrainian President Volodymyr Zelensky that is at the center of a whistleblower complaint filed in August.

Trump has denied saying anything inappropriate during his phone call with Zelensky, and he suggested in a closed-door meeting last month that the whistleblower was "almost a spy."

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President Donald Trump on Sunday heightened his attacks on Democrats who are pursuing an impeachment inquiry against him, accusing both House Speaker Nancy Pelosi and Rep. Adam Schiff of treason.

Pelosi announced last month that the House would launch a formal impeachment inquiry into Trump's activities — in particular, the July 25 phone call between Trump and Ukrainian President Volodymyr Zelensky that is at the center of an August whistleblower complaint.

The intelligence official who lodged the complaint detailed concerns that Trump had pressured Ukraine to aid him politically by investigating former Vice President Joe Biden and his son on allegations of corruption.

The complaint was declassified last month, and the White House released a memo summarizing the call that appeared to corroborate it.

Trump on Sunday night lashed out at Pelosi and Schiff, the chairman of the House Intelligence Committee who has been tasked with leading the impeachment investigation.

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

"Nancy Pelosi knew of all of the many Shifty Adam Schiff lies and massive frauds perpetrated upon Congress and the American people," he wrote.

"This makes Nervous Nancy every bit as guilty as Liddle' Adam Schiff for High Crimes and Misdemeanors, and even Treason. I guess that means that they, along with all of those that evilly 'Colluded' with them, must all be immediately Impeached!"

Schiff has characterized Trump's call with Zelensky as a "classic Mafia shakedown of a foreign leader."

Trump denies saying anything inappropriate during his phone call with Zelensky, and he suggested in a closed-door meeting last month that the whistleblower was "almost a spy."

Trump also accused Schiff of committing treason in a tweetstorm last week and demanded to meet with his accuser, whose identity is kept secret under whistleblower laws.

Schiff said last month that the whistleblower had agreed to testify before Congress and that the testimony was expected "very soon" once security measures were in place to protect the person's identity.