One potential thorn in Senator Obama’s side is die-hard Clinton supporters who say they would rather vote for Senator McCain, or not vote at all, than cast a ballot for Mr. Obama in November.

“People are very disappointed. They feel the party hasn’t stood up to her,” one such supporter, Linda Leest, 64, said Tuesday evening at a rally in New York City for Senator Clinton. Ms. Leest said she would vote Democratic down the ticket this year, as she has for 45 years, but that she would not pull the lever for Mr. Obama.

“I would possibly vote for McCain. Definitely not Obama,” another Clinton volunteer, Marta Alexander, said. “We don’t drink lattes, and we don’t drink the Obama Kool-Aid.”

While Mr. Obama celebrated securing the Democratic presidential nomination, and many of the Clinton campaign’s most loyal surrogates acknowledged that her chances at victory had passed, many of her grassroots supporters would not take no for an answer, at times chanting, “No Hillary, no vote!”

The “Hillary or nobody” stance underscores divisions reflected in exit polls from recent primaries. In strong Clinton states such as Kentucky and West Virginia, about two-thirds of her voters said they would vote for Mr. McCain, the presumptive Republican nominee, or stay home in November if Mr. Obama won the nomination, CNN polls showed. While recent states’ electorates have proved to be less polarized, potential problems remain: Nearly half of Clinton voters in Montana and South Dakota on Tuesday said they would be dissatisfied if Mr. Obama won the nomination, the Associated Press reported.

Some of Mrs. Clinton’s surrogates have suggested that Mr. Obama choose her as his running mate to consolidate the party’s base. Rep. Nydia Velázquez, a Clinton supporter who represents parts of Brooklyn, Queens, and Manhattan, said Mrs. Clinton could help Mr. Obama in particular to attract Latino voters.

“Even in the early primaries to the last primary that was conducted in Puerto Rico, she won overwhelmingly,” Ms. Velázquez said, when asked about Mr. Obama’s appeal to the Latino community. “So something wasn’t working or is not working, and I think she would be able to help in that regard.”

Mr. Obama has yet to signal publicly whether he is considering Mrs. Clinton as his vice presidential pick, and with five months remaining until the general election and emotions running high, it is unclear how many of the former first lady’s supporters will make good on threats to stay home on election day or vote for Mr. McCain.

One Clinton supporter at Tuesday’s rally, Laura Ramirez, said she was not sure whether she could bring herself to support Mr. Obama in November.

“I’m not sure if I would vote for him, but I would not vote for McCain,” Ms. Ramirez, a finance student at Baruch College, said. “I guess it will come down to the lesser of two evils.”