US President Donald Trump has sent a letter to House Speaker Nancy Pelosi to lash out the impeachment process being pushed ahead by the Democrats.

The lengthy, six-page letter is dated Tuesday. The following day, the Democrats hope to vote in favor of two articles of impeachment against Trump in the House of Representatives.

Trump started the letter, "I write to express my strongest and most powerful protest against the partisan impeachment crusade being pursued by the Democrats."

He said the first article of impeachment, "Abuse of Power," is "a baseless invention of your imagination."

As for the second article, "Obstruction of Congress," he called it, "preposterous and dangerous."

He described the impeachment as "nothing more than an illegal, partisan attempted coup." He added that the voters are wise, and that they will hold Pelosi and the Democrats responsible in the 2020 election.

Trump also told reporters on the same day at the White House that, "the whole impeachment thing is a hoax."

He said he looks forward to the Senate trial. He criticized the impeachment process in the House, saying his side was not entitled to lawyers, witnesses, or anything else.