If the House votes as expected on Wednesday along party lines, Mr Trump will become the third president in US history to be impeached.
He will then go on trial in the Senate, where Senators from both parties are obliged to act as independent jurors.
The Senate is controlled by the president’s Republican Party. Republican Senate Leader Mitch McConnell outraged Democrats last week when he said Republican senators would act in “total co-ordination” with the president’s team during the trial and vote against the process.
Mr Trump is facing two impeachment charges: obstruction of Congress, by refusing to co-operate with the impeachment probe, barring staff from testifying, and holding back documentary evidence; and attempting to use his office to pressure Ukraine to investigate his Democratic political rival Joe Biden.
Chuck Schumer, the Democratic Minority Senate Leader, said: “If articles of impeachment are sent to the Senate, every single senator will take an oath to render ‘impartial justice’. Making sure the Senate conducts a fair and honest trial that allows all the facts to come out is paramount.”
Earlier on Tuesday, Mr Trump’s personal lawyer Rudy Giuliani appeared to confirm that he worked to remove the US ambassador to Ukraine, Marie Yovanovitch, to clear the way for investigations that could be politically useful to Mr Trump.
Mr Giuliani told the New York Times he passed along to Mr Trump “a couple of times” information about how Ms Yovanovitch had got in the way of potential investigations.
“I needed Yovanovitch out of the way,” Mr Giuliani told the New Yorker magazine.