Speaking at a political rally in Lake Charles, Louisiana, Trump said, "They know they can't win on Election Day so they're pursuing an illegal, invalid and unconstitutional, bullshit impeachment." House Democrats launched an impeachment inquiry to investigate Trump after a U.S. intelligence official filed a whistleblower's complaint about a July 25 call between the U.S. president and Ukrainian President Volodymyr Zelenskiy.
In the call, Trump pressed Zelenskiy to investigate his political rival Joe Biden, a former U.S. vice president and a leading candidate seeking the 2020 Democratic presidential nomination.
The whistleblower's complaint also raised concerns about the classification of the call and other calls between Trump and foreign leaders.
The investigation could lead to the approval of articles of impeachment - or formal charges against the president - in the House.
A trial on whether to remove Trump from office would then be held in the Senate, where Trump's fellow Republicans who control the chamber have shown little appetite for ousting him.