Mary Commanday has appealed for an end to what she described as the “opportunistic and cynical use” of events in the Libyan city of Benghazi by the Trump campaign.

Mr Stevens was killed when Islamic militants stormed the US diplomatic compound in September 2012 when Hillary Clinton was Secretary of State.

His death and that of three other Americans in Benghazi has been repeatedly cited by the Trump campaign as evidence of Mrs Clinton’s lack of judgment and integrity.

In one of his many tweets, Donald Trump wrote: “If you want to know about Hillary Clinton's honesty and judgment, ask the family of Ambassador Stevens.”