One of former President George W Bush’s key foreign policy chiefs has endorsed Hillary Clinton over Donald Trump in a dramatic sign that the presumptive Republican presidential nominee is being abandoned by the party’s national security establishment.

Richard Armitage, who was deputy secretary of state from 2001 until 2005, said he would vote for Mrs Clinton, the presumptive Democratic nominee, in November’s election because he did not believe Mr Trump is a Republican. He also suggested Mr Trump was uninformed.

“If Donald Trump is the nominee, I would vote for Hillary Clinton,” Mr Armitage told Politico. “He doesn't appear to be to be a Republican, he doesn't appear to want to learn about issues. So I’m going to vote for Mrs. Clinton.”