Secretary of State Mike Pompeo used to be a staunch critic of President Donald Trump.

In 2016, Pompeo warned Trump would be an "authoritarian president" who ignores the Constitution.

The president has turned a number of former critics into key allies.

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In March 2016, then-Rep. Mike Pompeo of Kansas issued a stark warning about Donald Trump.

Trump's presidential campaign was rapidly gaining momentum and it was beginning to unnerve the Republican establishment. The real estate mogul had gone from a target of ridicule to a serious contender for the 2016 GOP presidential nomination.

At the time, Pompeo had endorsed Sen. Marco Rubio of Florida for president. On the day of the Kansas caucus, Pompeo delivered remarks characterizing then-President Barack Obama as an "authoritarian" and warning Trump would be the same.

"I'm going to speak to you from the heart about what I believe is the best path forward for America," Pompeo said, before going on to reference when Trump claimed if he ordered a soldier to commit a war crime the soldier would "go do it."

"We've spent 7.5 years with an authoritarian president who ignored our Constitution. We don't need four more years of that," Pompeo said in reference to Trump in a video clip that resurfaced alongside a sweeping New Yorker profile of the secretary of state.

—The New Yorker (@NewYorker) August 19, 2019

GOP Sen. Ted Cruz of Texas ultimately won the 2016 Kansas Republican caucus, with Trump in second and Rubio in third. The Florida senator dropped out of the race not long after.

Meanwhile, Pompeo continued to be critical of Trump along the campaign trail. In April, he told the the Capital-Journal in Topeka that Trump was "not a conservative believer," and a few weeks later told CNN that a lot of Trump's policies "don't comport with my vision for how I represent Kansas." By May, Pompeo endorsed Trump, albeit reluctantly.

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Pompeo, an Army veteran, would go on to serve as CIA director under Trump before becoming secretary of state. He's now one of Trump's most loyal and trusted advisers, despite his past criticism of the commander-in-chief. Pompeo has reportedly been considering a Senate run in Kansas.

But the secretary of state is hardly the only senior member of Trump's administration who's been critical of the president in the past.

White House counselor Kellyanne Conway, for example, spent much of the 2016 presidential primary season attacking Trump on cable news and describing him as "unpresidential" and someone who uses "vulgar" language that's "unfortunate for children."

The president has turned a number of former critics into key allies, including lawmakers like GOP Sen. Lindsey Graham of South Carolina, who in 2015 referred to then-candidate Trump as a "race-baiting, xenophobic religious bigot." Today, Conway and Graham, much like Pompeo, are among the first to stand-by Trump when he sparks controversy with his rhetoric or policies.