Richard Armitage, who held top national security positions in the administrations of former Presidents George W. Bush and Ronald Reagan, said he would vote for presumptive Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE over her likely Republican rival, Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE.

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"If Donald Trump is the nominee, I would vote for Hillary Clinton," Armitage, who served as a deputy secretary of State under Bush and as an assistant secretary of Defense under Reagan, told Politico on Thursday.

"He doesn't appear to be a Republican. He doesn't appear to want to learn about the issues. So I'm going to vote for Mrs. Clinton."

Clinton hit Trump earlier this month on national security, saying his ideas would put America in greater danger and inspire more terrorist attacks.

"A ban on Muslims would not have stopped this attack," Clinton added on Wednesday, referring to the mass shooting at a gay nightclub in Orlando, Fla. over the weekend.

"Neither would a wall. I don't know how one builds a wall to keep the internet out," she said. "Not one of Donald Trump's reckless ideas would have saved a single life in Orlando."

--This report was updated at 12:32 p.m.