Treasury Secretary Steven Mnuchin and House Financial Services Committee Chairwoman Maxine Waters (D-Calif.) engaged in a fierce clash Tuesday, squaring off amid rising antagonism between the White House and congressional Democrats.

Their disagreement appeared to be over something innocuous — how long Mnuchin would continue to testify at a hearing — but Waters refused to budge and Mnuchin became furious when he wasn’t dismissed more than three hours after the hearing began.

When Waters told Mnuchin he was free to get up and leave, Mnuchin appeared nervous, unsure what that would mean.

“Please dismiss everybody,” Mnuchin said, he then mispronounced the wooden mallet she held in her hand.

“I believe you are supposed to take the gravel [sic] and bang it,” he said.

Waters snapped back at him immediately.

“Please do not instruct me as to how I am to conduct this committee,” she said.

House Democrats spent much of the day peppering Mnuchin with a range of questions. His testimony before Waters’s committee was his second House hearing of the day.

He fielded numerous questions about whether he would release Trump’s tax returns (he wouldn’t say whether he would), and he also was asked about his personal ethics disclosures and the treatment of Russian companies.

As the afternoon hearing dragged on, Mnuchin said he needed to leave by 5 p.m. so that he could attend a meeting with an important foreign leader. He would later reveal it was a senior official from Bahrain to discuss “national security.”

Waters didn’t appear impressed.

“We’re all late all the time, unfortunately,” she said. “We’re all pressed for time, and I do get it.”

A number of the Democrats and Republicans on the committee still had not been able to ask Mnuchin questions, and she wanted Mnuchin to agree to come back twice in May for more time. He seemed exasperated at the request and wouldn’t agree to it. It was 5:15 p.m., and he said his meeting was scheduled to begin at 5:30 p.m.

“When the Republicans [controlled the House of Representatives last year], they did not treat the secretary of the Treasury this way,” Mnuchin said. “So if this is the way you want to treat me, then I will rethink whether I would voluntarily come back here later to testify, which I have offered to do.”

Waters again said Mnuchin could leave whenever he wanted. He wouldn’t get up until she adjourned the committee, and grew angrier and angrier.

“You are instructing me, you are ordering me to stay here,” he said.

Mnuchin said no treasury secretary had testified before Congress for longer than three hours and 15 minutes in the past six years. He seemed to anticipate that this was going to be an issue, as he had a notecard in his pocket with the length of testimony for each treasury secretary over the past six years.

Waters swatted away the precedent.

“This is a new way, and it’s a new day,” she said. “And it's a new chair, and I have the gavel. At this point, if you wish to leave, you may.”

Mnuchin ultimately agreed to stay. He did leave at 5:30, and by that point he seemed to have cooled off a bit.

“Thank you and I look forward to being back in May; we’ll work on a date,” Mnuchin said as the hearing ended.