Mr. Lauder, the president of the World Jewish Congress who recently started a new $25 million effort to fight anti-Semitism that employs a pollster working for Mr. Bloomberg, listened as Mr. Trump ticked off a litany of administration actions. Mr. Trump said that he had done more for Jews than any other president and that he could still lose the Jewish vote. The president never mentioned campaign contributions, but advisers and others briefed on the call said he left the clear impression that was referring to financial support.

In a statement, Mr. Lauder would say only that he has had “many candid, positive and forward-looking conversations with” Mr. Trump, who “deserves a great deal of support from the Jewish community for his fantastic record on Israel and his proven support of the Jewish people here at home.”

Then it was time to get back to White House work, and Mr. Trump huddled with advisers offering him a range of options on how to respond to the death of an American civilian contractor killed on Dec. 27 in a rocket attack on an Iraqi military base. The menu of choices included the most extreme one — killing Maj. Gen. Qassim Suleimani, Iran’s most powerful commander.

On New Year’s Eve, Mr. Trump hosted his annual party at Mar-a-Lago, arriving in a tuxedo with the first lady, Melania Trump, and playing M.C. to a crowd that included his personal lawyer Rudolph W. Giuliani.

On Jan. 2, the president began his day at his golf club. But mindful of not appearing weak in the face the rocket attack and concerned that an assault on the American Embassy in Baghdad that United States officials said was orchestrated by Iran could have ended in devastation, Mr. Trump had already settled on a course of action.

In the middle of a meeting with campaign advisers, he left the table to give the final authorization to kill General Suleimani. The president then returned, and, compartmentalizing what had just happened, resumed talking about the campaign.

It was an act of enormous consequence, but the White House made no public statement for hours, though the president cryptically tweeted about what had taken place. Whatever the administration’s objectives were, and whatever intelligence they had used to justify the strike, it was not being shared in any conventional fashion.