In recent days, it had been unclear whether Mr. Sanders intended to stay in the race, and even on Sunday he did not rule out the possibility that he would formally concede the nomination in the coming days.

After he met with Mr. Obama on Thursday he said he looked forward to exploring how he could work with Mrs. Clinton “to defeat Donald Trump and to create a government which represents all of us and not just the 1 percent.” Then he held a rally that night in Washington urging voters to cast ballots for him on Tuesday in the nation’s final primary.

When asked by Chuck Todd on Sunday’s “Meet the Press” on NBC whether he was an “active candidate,” he responded that he wanted to see Mr. Trump defeated.

Mr. Sanders said that he and Mrs. Clinton planned to meet on Tuesday and that he would ask her “whether she will be vigorous in standing up for working families in the middle class, moving aggressively in climate change, health care for all, making public colleges and universities tuition-free.”

“And after we have that kind of discussion and after we can determine whether or not we are going to have a strong and progressive platform,” he said, “I will be able to make other decisions.”

There have been signs that he was winding down his run. While Mrs. Clinton has been hiring campaign workers, Mr. Sanders started laying off at least half of his campaign staff members last week. He has let go of a number of advance staff members who help with campaign logistics, as well as field workers who have been canvassing for votes.

According to a person who attended the meeting at Mr. Sanders’s home Sunday, and who spoke on condition of anonymity to describe a private gathering, there was no talk from Mr. Sanders about trying to win the nomination. The group was keenly interested in how the senator’s meeting with Mrs. Clinton on Tuesday will turn out, and whether he would get assurances that she would fight for his ideas, this person said.

While he is effectively no longer a threat, Mrs. Clinton and the Democrats are counting on Mr. Sanders to eventually get behind her candidacy. He has a loyal base of more than 10 million voters and an enormous donor list that Mrs. Clinton will want to tap into. Some of his supporters say they will not vote for anyone but Mr. Sanders, so Mrs. Clinton’s success may depend on how vocally the senator supports her.