WATCH: Why Five Important Trump Allies Finally Turned Against Him

Some Republicans who were blistering critics of President Donald Trump during the 2016 presidential election have since turned into devoted supporters, including Sen. Lindsey Graham of South Carolina, Sen. Ted Cruz of Texas and Sen. Marco Rubio of Florida. But with some other prominent Republicans, the opposite is true: they went from being Trump allies to being vehement critics. Amanda Carpenter, a Never Trump conservative who formerly served as Cruz's communications director, takes a look at some of those defectors in an article published in The Bulwark on September 14 and explains the reasons for their defections.

"For all the loyalty Donald Trump enjoys from his most sycophantic followers, many prominent figures who famously assisted him have given up on the president altogether," Carpenter explains in her article. "It's worth taking a look at the breaking points for these various White House staffers, cabinet secretaries, political advisers and others — the moment when each decided he or she just couldn't stick with Trump anymore. Because we can learn a lot about Trump and the overall effect he is having on our country by studying what made these individuals — from revered military leaders to Trump's sleazy surrogates — finally snap."

Here are five of the former Trump allies who, according to Carpenter, reached a breaking out.

1. Elizabeth Neumann

In 2016, conservative Republican Elizabeth Neumann voted for Trump. But now, Neumann — who served as assistant secretary for counterterrorism and threat prevention at the U.S. Department of Homeland Security under Trump — is making no secret of the fact that she plans to vote for former Vice President Joe Biden in 2020's presidential election. And she endorsed Biden in an anti-Trump attack ad by the group Republican Voters Against Trump.

Neumann, Carpenter notes, has stressed that a white nationalist's August 2019 terrorist massacre at a Walmart in El Paso, Texas did a lot to turn her against Trump. The shooter killed more than 20 people, mostly Latino, in response to what he called the "Hispanic invasion of Texas." Carpenter told The Bulwark, "The point at which my position changed and I said 'No, at this point, you are culpable' was after El Paso…. Post-El Paso, there is no excuse."

2. John Bolton

John Bolton was an odd choice for Trump's national security director: while Trump has been greatly influenced by the isolationist and hypernationalist Patrick Buchanan, Bolton is a devout neocon and an unapologetic war hawk. Nonetheless, having Bolton in his administration was a way for Trump to thumb his nose at liberals — that is, until Bolton reached the point where he could no long stomach Trump's foreign policy views. Bolton, Carpenter observes, "decided he had to leave in September 2019, after Trump made plans to invite the Taliban to Camp David public."

Bolton, Carpenter notes, has said of Trump, "The day after the election, whether Trump wins or loses, we face a real debate — maybe an existential debate — about what the future of the Republican Party is. I just think it's important for the Republican Party to separate itself from Trump and for the conservative philosophy to separate itself from Trump."

3. Gen. James Mattis

Like Bolton, former Defense Secretary James Mattis left Trump's administration because of the president's views on foreign policy. Carpenter explains, "Mattis walked out on Trump in December 2018 when the president ignored his advice and abruptly pulled troops out of the Middle East. Mattis is quoted in Bob Woodward's new book, Rage, as saying, 'When I was basically directed to do something that I thought went beyond stupid to felony stupid, strategically jeopardizing our place in the world and everything else, that's when I quit.'"

4. Miles Taylor

Miles Taylor, who served as chief of staff at DHS, told The Bulwark, "The total tonnage of bad Trump ideas that never materialized were enough to crush anyone's hopes about a successful presidency. But the one that broke my desire to continue serving was his perverse insistence on resuming family separation at the border — and making it worse. It was sick, wrong, and un-American. That's when it became clear that saying 'no' to Trump was no longer enough."

Like Neumann, Taylor has appeared in a pro-Biden ad from Republican Voters Against Trump: