Rep. Adam Kinzinger Adam Daniel KinzingerFox News reporter defends confirming Atlantic piece despite Trump backlash: 'I feel very confident' GOP lawmaker defends Fox reporter after Trump calls for her firing Lindsey Graham: 'QAnon is bats--- crazy' MORE (R-Ill.) directly challenged Defense Secretary Mark Esper Mark EsperOvernight Defense: Stopgap spending measure awaits Senate vote | Trump nominates former Nunes aide for intelligence community watchdog | Trump extends ban on racial discrimination training to contractors, military Overnight Defense: Pentagon redirects pandemic funding to defense contractors | US planning for full Afghanistan withdrawal by May | Anti-Trump GOP group puts ads in military papers Official: Pentagon has started 'prudent planning' for full Afghanistan withdrawal by May MORE during a closed-door GOP meeting over President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE’s controversial decision to pull U.S. troops out of Syria, Republican sources told The Hill.

Kinzinger has been extremely critical of Trump’s actions in Syria in both tweets and media appearances. But GOP lawmakers in Tuesday evening’s meeting say they sat up in their seats when Kinzinger, an Iraq and Afghanistan war veteran, went to the microphone and voiced frustration and anger to Esper over the Syria issue.

ADVERTISEMENT

“Kinzinger let Esper know exactly how he felt about the Syria decision and the damaging, deadly repercussions it will have,” said a Republican source familiar with the exchange, which occurred at the weekly GOP whip meeting hosted by Majority Whip Steve Scalise Stephen (Steve) Joseph ScaliseGinsburg becomes the first woman to lie in state in the Capitol House GOP slated to unveil agenda ahead of election House panel details 'serious' concerns around Florida, Georgia, Texas, Wisconsin elections MORE (R-La.).

Neither Kinzinger’s office nor the Pentagon had any comment. Republicans described the meeting to CNN as “a little heated,” with one lawmaker calling Trump’s Syria move “the worst foreign policy decision of my lifetime.”

Kinzinger has been one of the most vocal GOP critics of Trump’s decision to withdraw troops from northern Syria — a move that has allowed Turkey to launch deadly military strikes against Kurdish forces that assisted the U.S.-led fight against ISIS.

“@realDonaldTrump I thought you were going to defeat ISIS, that is why people voted for you. What changed? This is weakness. America is far more honorable than this,” Kinzinger tweeted at Trump after he announced his Syria decision.

“How is reconstituting ISIS, abandoning the Kurds, and green lighting a slaughter by the Turks not our concern?” Kinzinger tweeted earlier Wednesday.

The meeting with Esper came a day before the House voted 354 to 60 to pass a resolution rebuking Trump’s decision to pull troops out of Syria and condemning Turkey’s attacks on the Kurds.

Scalise had invited Esper to speak at the whip meeting weeks ago, before Trump set his new policy in Syria. But because of the urgency of the issue, the Syria withdrawal and Turkey's aggression quickly became the focus of the private gathering in the basement of the Capitol.

Earlier this year, Kinzinger, a lieutenant colonel in the Air National Guard, had pitched himself to become Trump’s secretary of the Air Force. But Trump nominated Barbara Barrett, a businesswoman and former diplomat, instead. The Senate confirmed her nomination Wednesday in an 85-7 vote.

Rebecca Kheel contributed.