Acting Defense Secretary Patrick Shanahan clashed with U.S. lawmakers during a private briefing on President Trump’s plan to pull American troops out of Syria. The confrontation puts at risk Shanahan’s chances of becoming the official head of the Pentagon.

It happened during last weekend’s Munich Security Conference in Germany.

Sen. Lindsey Graham (R-SC), leader of the Congressional delegation to the conference, was particularly incensed by Shanahan’s testimony that Trump wants all U.S. forces out of Syria by April 30, according to NBC News.

Graham responded with an expletive, reports Washington Post columnist Josh Rogan, calling the withdrawal plan “the dumbest f—-ing idea I’ve ever heard.”

Graham then listed consequences he fears could result from so abrupt a U.S. withdrawal, including a resurgence of the battered Islamic State and a Turkish attack on U.S.-backed Kurdish forces.

“That could very well happen,” Shanahan said.

Graham then declared himself Shanahan’s “adversary” on the matter — and, reports NBC, “Shanahan shot back at Graham, asking if he has any more questions ‘as an adversary.’”

At that, writes Rogan, “several other lawmakers from both parties chimed in, warning Shanahan of what they believed were the risks” of the withdrawal plan. Shanahan remained silent except to repeat that he was following Trump’s instructions.

As for what happens if Trump nominates Shanahan for Secretary of Defense, Rogan says a Democratic congressman told him, “If this was an audition for the job full time, he failed.”