Miles Taylor, the former DHS chief of staff under President Trump, endorsed Joe Biden for president Monday, saying Trump "wanted to exploit the Department of Homeland Security for his own political purposes and to fuel his own agenda."

Why it matters: Taylor joins other prominent Republicans who have publicly said they will either not vote for Trump's re-election this November or will back Biden.

Not voting for Trump:

• Sen. Mitt Romney (Utah): The party's 2012 presidential nominee said in February that he will not support Trump shortly after he voted to convict the president on one count in his impeachment trial.
• John Bolton: Trump's former national security adviser said he will not vote for Biden or Trump and hopes that history remembers Trump "as a one-term president."
• Jeff Flake: The Arizona Senator said he will not vote for Trump, but added that he's never voted for a Democrat for president, per The Washington Post.
• William H. McRaven: McRaven, who led the raid that killed Osama bin Laden, has publicly criticized the president. He told The New York Times, "This fall, it's time for a new leadership in this country — Republican, Democrat or independent."

Voting for Biden:

• Colin Powell: The former secretary of state under George W. Bush and retired four-star general said that he will support Biden because he believes that Trump has "drifted away" from the Constitution.
• Carly Fiorina: The 2016 presidential candidate said she will support Biden because she believes he is "a person of humility and empathy and character," per The Atlantic.
• John Kasich: The former Ohio governor and 2016 presidential candidate is not only endorsing Biden, but also speaking at the DNC to support the former vice president.
• Miles Taylor: The former Department of Homeland Security chief of staff officially endorsed Biden saying, "Even though I'm not a Democrat, even though I disagree on key issues, I'm confident that Joe Biden will protect the country."

On the fence:

• Sen. Lisa Murkowski (Alaska): Murkowski, one of Trump's consistent foils in the Senate, said that she was "struggling" to support the president's re-election after James Mattis, the former defense secretary, issued a public rebuke.

Undecided publicly but skeptical, via a New York Times report:

• George W. Bush: The former president has reportedly decided not to support Trump's re-election, though he's made no public statements to that end.
• Jeb Bush: The former Florida governor and 2016 presidential candidate is so far reportedly undecided.
• Cindy McCain: The widow of the late Sen. John McCain (Ariz.) will reportedly vote for Biden, but remains unsure how public to be about it.

Worth noting: While former top military leaders like Mattis and John Kelly are technically non-partisan, they both served in Trump's administration and have publicly expressed skepticism about the president's standing ahead of the 2020 election.

• Mattis said Trump made a "mockery of our Constitution" and called him "the first president in my lifetime who does not try to unite the American people" after the president's response to mass protests in the wake of George Floyd's killing.
• Kelly, Trump's former chief of staff and homeland security secretary, said he agreed with Mattis' comments.

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Editor's note: This article has been updated with the latest Republicans to back Biden.