Donald Trump’s mockery of a woman accusing his Supreme Court nominee of sexual assault appeared to backfire on Wednesday as three key wavering Republican senators criticised the comments.

The US president parodied the testimony of Christine Blasey Ford, a California professor making the claim who has admitted to not remembering significant details about the alleged incident.

Jeff Flake, the senator from Arizona, said the remarks were “appalling”, Susan Collins of Maine called them “just plain wrong” and Lisa Murkowski of Alaska said it was “wholly inappropriate”.

A vote on Brett Kavanaugh’s nomination to America’s top court is expected later this week after the FBI completes its investigation but the result hangs in the balance. If just two Republican senators voted no, his candidacy would likely be defeated.

Mr Trump had initially avoided criticism of Prof Ford, who accused Mr Kavanaugh of pinning her on a bed and groping her at a high school house party in 1982, calling her a “very credible witness” after she gave testimony to a Senate committee last week.

However addressing a crowd of cheering supporters at a rally in Southaven, Mississippi, on Thursday night, Mr Trump adopted a mocking tone and pointed to gaps in her memory of the alleged incident.