Scowcroft said Clinton has the "wisdom and experience to lead our country at this critical time," mentioning her time as secretary of State, New York senator and first lady.

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"She has spent her entire career in public service working to improve the lives of the American people, and helping the United States lead a more secure and peaceful world," he said.

Scowcroft said the presumptive Democratic presidential nominee "shares my belief that America must remain the world's indispensable leader."

Richard Armitage, the deputy secretary of State under George W. Bush, said last week he'd vote for Clinton, saying Trump "doesn't appear to want to learn about the issues."

The Bush family has shied away from discussing Trump publicly since Jeb Bush dropped out of the GOP race in February. An aide said in May that George W. Bush didn't "plan to participate in or comment on " the race.

George W. Bush has since signaled plans to aide vulnerable GOP incumbents who could be hurt by Trump. The New York Times reported last week Bush was bothered by many of Trump's remarks, particularly about Muslims and immigrants.

George H.W. Bush and George W. Bush are not attending the GOP convention next month.