Mr. Trump, according to people close to the president, had been openly talking about firing Mr. Comey for at least a week. Despite the objections from some of his aides about the optics and the lack of an obvious successor, the grumbling evolved into a tentative plan as he angrily watched the Sunday news shows at his Bedminster, N.J., golf resort.

By Monday, capping off months of festering grievances, Mr. Trump told people around him that he wanted Mr. Comey gone, repeatedly questioning Mr. Comey’s fitness for the job and telling aides there was “something wrong” with him, several people familiar with the discussions said…

The chief strategist Stephen K. Bannon, who has been sharply critical of the F.B.I., questioned whether the time was right to dismiss Mr. Comey, arguing that doing it later would lessen the backlash, and urged him to delay, according to two people familiar with their thinking. Reince Priebus, the White House chief of staff, had voiced similar concerns, but was more supportive of the move when Mr. Trump brushed aside aides’ objections.

Mr. Trump was adamant, denouncing Mr. Comey’s conduct in both the Clinton and Russia investigations, and left aides on Monday with the impression that he planned to take action the next day.