WASHINGTON: "Everyone knows she's a Marxist," Republican presidential hopeful Donald Trump has repeated loudly and often, referring to his Democratic rival Kamala Harris, who he is hoping to tar with one of the oldest brushes in the US political playbook.

The aim? To portray Harris as a dangerous left-wing extremist, and to invoke the infamous Cold War-era "red scare" in the United States.

In recent weeks, the former president has stepped up his rhetoric against the vice president, describing her as both a "Marxist" and a "communist" at almost every opportunity.

Harris has not directly addressed the taunts, but her policies over decades of holding public office do not appear to conform to either the 19th-century German theorist's views or the various left-wing schools of thought that followed him.

"She's not a Marxist, she's not a communist," said Thomas Zeitzoff, a professor at American University and a specialist on political violence.

For the Republican camp, using such terms is "a way of trying to say that she's extreme," he told AFP.

Trump, experts say, is using an age-old US political tactic called "red baiting," which aims to discredit an opponent by accusing them of not being a capitalist.