He claimed the US vice-president is in "big trouble" for insulting her rival, but justified the Republican nominee calling Harris "crazy".
The culture secretary said "we’ve had far too much people using negative language towards one another".
The former UK ambassador to the US suggested this row is not a "political crisis" but a "political game".
The prime minister has insisted the UK will not pay compensation - or apologise - for its historic role in the slave trade.
In a CNN town-hall-style event, the Democratic presidential nominee homed in on reports from former Trump aides about his authoritarian tendencies.
The former White House chief of staff said he believed Donald Trump meets the definition of a fascist and would be dangerous if elected president again.
"He put his hands all over my breasts, my waist, my butt," former model Stacey Williams said of the Republican nominee for president, according to the Guardian.