The news was first reported by The Huffington Post’s Jessica Schulberg and tweeted Saturday by Kristina Schake, Kori's sister and the deputy communications director for the Clinton campaign.
“Good people can and should try to work for him,” Kori Schake told HuffPost on the topic of Trump. “But I am deeply skeptical that these people who go to work for Trump will be able to have any influence over his policies.”
“What I think is more likely than a reconciliation with Trump by conservative foreign policy and defense policy experts,” she added, “is a slow, agonizing reconciliation that Hillary Clinton is a safer pair of hands.”
After serving as the director for defense strategy and requirements on the National Security Council during Bush's first term, Schake was a senior policy adviser to Sen John McCain (R-Ariz.) during his 2008 presidential bid. She is currently a research fellow at Stanford University's Hoover Institution.
She was one of more than 100 Republicans to sign a letter in March vowing not to vote for Trump.
Other former Bush officials to announce their support for Clinton include former Treasury Secretary Hank Paulson and former Deputy Secretary of State Richard Armitage.
"The GOP, in putting Trump at the top of the ticket, is endorsing a brand of populism rooted in ignorance, prejudice, fear and isolationism," Paulson wrote in an op-ed for The Washington Post. "This troubles me deeply as a Republican, but it troubles me even more as an American. Enough is enough. It’s time to put country before party and say it together: Never Trump."
This post has been updated with more quotes from Kori Schake.