Even Anderson Cooper has his limits.

The normally unflappable CNN anchor vented his frustration Friday afternoon by dropping a surprising scatological remark during a sparring session with political commentator Jeffrey Lord, a fervent Trump supporter.

Cooper was pressing Lord on whether it was appropriate for President Trump to tell Russian officials that his firing of FBI Director James Comey relieved pressure on his administration, but Lord attempted to sidestep the question. Cooper then blurted out, “If he took a dump on his desk, you would defend it.”

Lord was briefly taken aback, then laughed, while Cooper attempted to regain his composure.

“I mean, I don’t know what he would do that you would not defend,” Cooper continued. “I mean, you’re a loyal guy, I think that speaks well of you.”

Cooper later apologized on the air for being “a little crude,” and he followed up on Twitter after the show. “It was unprofessional,” he wrote. “I am genuinely sorry.”

Though Cooper is usually a pretty cool customer, he has clashed with Lord on several occasions and was recently driven to roll his eyes at White House adviser Kellyanne Conway.

See the exchange with Lord above.