Trump revives Cold War-era rhetoric, accusing Democrats of embracing a "communist menace" as Republicans prepare for the midterms.

US President Donald Trump is reviving Cold War-style warnings about communism, casting the Democratic Party as a red "menace" as Republicans hunt for a midterm message to hold their narrow grip on Congress.

The rhetoric, echoing the anti-communist crusades of the 1950s, has surged from Trump's speeches into the broader Republican campaign machine after a string of democratic socialist primary victories in New York and Colorado.

And it has grown apocalyptic, often overtaking the president's fixation on election fraud, as he frames November's vote as a civilizational clash between Republican "common sense" and left-wing extremism.

During weekend speeches at Mount Rushmore and in Washington marking America's 250th anniversary, Trump warned of a communist "menace" that needed to be cut out "like a cancer."