Support has been building for such a move over recent months.

But it was the details of the president's phone call with the Ukrainian leader that escalated the issue.

There is now widespread support among Democrats in the lower house for impeachment - more than 145 out of 235 members are in favour.

On Monday night, seven freshman Democrats, writing in the Washington Post, said that if Mr Trump had acted improperly in his conversation with Ukraine's president, it would "represent an impeachable offence".

More Democrats came forward on Monday and on Tuesday.

Long-serving Democrat and civil-rights icon John Lewis spoke in support of impeachment proceedings earlier on Tuesday.

He said in an impassioned speech that "now is the time to act... the future of our democracy is at stake".