“The language that was used, the attitude of the president, the expressions he made when it came to immigration just stunned me,” Mr. Durbin said.

Mr. Durbin, who has been in Congress for more than three decades and is no stranger to political back rooms, said the meeting was not the usual case of salty language shared among politicians gathered behind closed doors.

“It was beyond, and the intensity of the president’s feeling, and what he said there, as well as many other epithets during the course of it, I was surprised and shocked in a way,” he said, noting that upon his return to the Capitol, some colleagues commented on his demeanor.

“They said, ‘You look shaken,’ and I said I was,” he said. “After you have been in politics as long I have, it takes something to shake you up.”

Mr. Durbin said he did not personally leak details of the conversation and also directed his staff not to discuss it. But he did share his version of events with four other senators as they plotted how to proceed. Word of what happened during the meeting — and one word in particular — quickly circulated and was first reported by The Washington Post within hours.

Mr. Durbin then began discussing the meeting in public the next morning while in Chicago after the White House did not deny reports of what transpired. The president and others attending the meeting only later challenged exactly what expletives were used in describing countries that Mr. Trump wanted to prevent from sending migrants to the United States.

Though the disclosure has roiled the negotiations, Mr. Durbin said it has also provided better context of the president’s immigration stance.