Security has been ramped up at the US Capitol in Washington in response to “a possible plot to breach” the building.
The move was prompted by intelligence that a militia group planned the attack for 4 March – the day conspiracy theorist group QAnon believes Donald Trump will return for a second term.
The House of Representatives cancelled Thursday’s session, but the Senate will continue with its agenda.
A mob loyal to Mr Trump stormed the Congress building in January.
That attack came as lawmakers were inside moving to certify Democrat Joe Biden’s election victory. Mr Trump still refuses to admit losing the election.
The riot saw five people including a police officer killed and shook the foundations of American democracy. The head of the Capitol police force later resigned.