Senator Bernie Sanders of Vermont grappled with tough and narrowing choices about campaign strategy and fund-raising on Wednesday after his crushing loss in the New York primary and with a series of difficult contests ahead.

While Hillary Clinton’s campaign carefully avoided any suggestion that he quit the Democratic presidential race, many of her prominent supporters argued that the moment had come for Mr. Sanders to ease off attacks for the good of Democrats in the November election.

Mr. Sanders, who took the day off to rest and regroup with his advisers, is under intense pressure to win the Pennsylvania primary on Tuesday or fall even further behind Mrs. Clinton’s sizable lead in pledged delegates needed to capture the nomination. A new Pennsylvania poll put Mr. Sanders 13 percentage points behind Mrs. Clinton, despite heavy spending by the Sanders campaign on television advertisements. Another loss could hamper his formidable fund-raising, which Sanders advisers described as steady but not as strong as it could have been with a New York victory.

In addition to Pennsylvania, four other states hold primaries on Tuesday, and Sanders advisers say that all of the contests will be tough for them. While Mr. Sanders has a strong shot at winning the Indiana primary on May 3, given his popularity with white voters and independents there, he has limited opportunities to pick up many more delegates than Mrs. Clinton, according to several Sanders advisers.