Trump's tweet came shortly before House Speaker Nancy Pelosi announced that she was instructing House Democratic chairmen to draw up articles of impeachment.
Biden has said he won't testify voluntarily.
About an hour after Pelosi spoke, Trump reacted on Twitter.
"The Do Nothing, Radical Left Democrats have just announced that they are going to seek to Impeach me over NOTHING. They already gave up on the ridiculous Mueller “stuff,” so now they hang their hats on two totally appropriate (perfect) phone calls with the Ukrainian President.... ...This will mean that the beyond important and seldom used act of Impeachment will be used routinely to attack future Presidents. That is not what our Founders had in mind. The good thing is that the Republicans have NEVER been more united. We will win!," he said.
A top White House official said on Capitol Hill Wednesday that President Trump is demanding a full trial featuring live witnesses in the Senate chamber if and when the House sends over articles of impeachment to the Senate later this month.
After he arrived at the White House from his trip to London, President Trump tweeted late Wednesday night about his July 25 call with Ukrainian President Volodymyr Zelenskiy.
Trump tweeted that when he told Zelenskiy, “I would like you to do us a favor though” that the “us” referred to the United States.
House Democrats have alleged that Trump was asking Ukraine to investigate his political rivals for his own personal political benefit – not for the benefit of the United States.
When Trump last night noted that he brought up the U.S. attorney general, he neglected to mention that he later told Zelenskiy he wanted him to speak not only with U.S. Attorney General Bill Barr, but also with his own personal lawyer, Rudy Giuliani.