US lawmakers are set to meet on Wednesday to confirm Joe Biden’s victory in the presidential election amid protests from Trump supporters.
A joint session of Congress will count and confirm electoral college votes.
Some Republicans have pledged to support President Donald Trump’s efforts to overturn the result by formally objecting at the session, in a bid that is almost certain to fail.
Hundreds of National Guard members are being mobilised.
Supporters of Mr Trump have begun gathering in Washington DC to rally against the certification of his defeat, and counter-protests are expected.
In a tweet on Tuesday, Mr Trump announced that he would be speaking at the “Save America Rally” the following day.
He has refused to concede the 3 November election, repeatedly alleging fraud without providing any evidence.
He has also tried to throw doubt on the integrity of Tuesday’s senate run-off vote in the southern, traditionally Republican, state of Georgia. Projections by US TV networks suggest the Democrats have won one of the seats and are neck and neck for the second seat.
If the Democrats win both seats they will have control of the Senate – something that will help Mr Biden push forward his agenda after he is inaugurated as president on 20 January.