Many television commercials presented loving, committed gay and lesbian couples or endorsements from straight, respected people from unexpected corners of the community, like a firefighter in Maine.

The advocates benefited from a threefold advantage in fund-raising, with large donations in Washington State from Jeff Bezos of Amazon and his wife and from Bill and Melinda Gates, and large personal contributions to all four campaigns from Mayor Michael R. Bloomberg of New York. But most of the money came as small donations, raised nationally by gay-rights groups.

The most ardent opponents of same-sex marriage, led by evangelical Christians and the Roman Catholic Church, have vowed to redouble their defense of “natural marriage,” even comparing it to the continuing fight against legal abortion.

So far, these opponents say they do not believe that the national tide has shifted against them but rather that they allowed themselves to be badly outspent in liberal-leaning states.

“We lost by small margins in bastions of deep-blue America,” said Brian S. Brown, president of the National Organization for Marriage. He noted that 30 states have constitutional amendments banning same-sex marriage. He said he expected Indiana to vote on such an amendment in the next year or two, “and we will win.”

But some Republicans question whether their party should try to resist a seemingly unstoppable demographic trend. “The die is cast on this issue,” said Steve Schmidt, who advised the presidential campaigns of Senator John McCain and George W. Bush and has for years urged Republicans to accept same-sex marriage. “Why should we sign a suicide pact with the National Organization for Marriage?” Mr. Schmidt asked, saying the party should instead endorse the principles of federalism and let the states decide the matter.

Beyond seeking repeal of Oregon’s marriage amendment, rights activists feel they can win in a repeat ballot in California if the courts do not first invalidate Proposition 8, the 2008 referendum that banned same-sex marriage, but faces a legal challenge.