When asked about Mr. Devine’s remarks, the senator’s wife, Jane Sanders, pushed back in a MSNBC interview. “No, no. We assess on an everyday basis,” Ms. Sanders said. “Even if he had a string of wins, like eight in a row or he’s won states by landslide victories, nobody in the media and certainly not The New York Times has ever said he has a chance to win.”

Stu Loeser, who owns a media strategy firm and was a longtime spokesman for Mayor Michael R. Bloomberg of New York, said he had seen this sort of back and forth in campaigns involving Mr. Devine before. During Vice President Al Gore’s presidential campaign, Mr. Devine had a reputation as a strategist who would be upfront with the candidate.

“Every elected official needs two kinds of loyalists close to them. One kind are the people who are with them no matter what, agree with them no matter what, and help them execute their vision,” Mr. Loeser said. “And the other is an adviser who is able to stand up and tell the candidate what he or she needs to hear regardless of whether the candidate wants to hear it. Tad Devine had that role with Gore in 2000.”

Mr. Sanders has started to talk more openly about the possibility of not winning the Democratic contest. During a rally in Indiana he talked not just of his path to victory but discussed what he might do if he lost.

He stressed he was in the race to “win and become the Democratic nominee.” But he also said if he did not succeed he would try to get as many delegates as possible and “put together the strongest progressive agenda any political party has ever seen.”

Michael Briggs, a spokesman for Mr. Sanders, said in a statement that the campaign would keep on staff more than 300 workers focused on the remaining contests.