Photographer: Pablo Martinez Monsivais/AP

President Donald Trump’s chief of staff and his national security adviser engaged in a heated argument outside the Oval Office on Thursday, according to three people familiar with the episode.

The chief of staff, John Kelly, and the national security adviser, John Bolton, fought over immigration and border crossings, including the performance of the Homeland Security Department under Secretary Kirstjen Nielsen, one person familiar with the matter said. She was at the White House for meetings on Thursday, but the people disagreed about whether she witnessed the argument.

Bolton criticized DHS, and Kelly defended Nielsen, a former deputy whom he supported to replace him at the department. Two people described the exchange as less a shouting match than an intense argument. Kelly then stormed away, so upset that he uttered some profanities.

Bolton and Nielsen had a good conversation after Kelly and Bolton’s argument, a White House official said. Both believe the goal is to protect the border, the official said.

Trump has lately expressed fury about a large group of migrants who are traveling from Honduras toward the U.S. border. He vowed Thursday to deploy the military and shut down the Mexican border unless the migrants are turned back.

The clash is an indication that tension is flaring in the White House 19 days before midterm elections in which Republican control of Congress is at stake. The shouting match was so intense that other White House aides worried one of the two men might immediately resign. Neither of the men is resigning, the people said.

Trump is aware of the argument, the people said, even though the president told reporters he didn’t know about it before boarding Air Force One to travel to Montana for a campaign rally. He has recently sought to make immigration a more prominent political issue, blaming Democrats for increased numbers of migrants crossing the border.

After the confrontation was reported, White House Press Secretary Sarah Huckabee Sanders issued a statement indicating that there are no hard feelings among the president’s senior advisers. The statement didn’t address the specific details of the argument.

“While we are passionate about solving the issue of illegal immigration, we are not angry at one another,” Sanders said, adding “our Administration is doing a great job on the border.”