In California, same-sex marriage has such overwhelming support today that Prop 8 almost certainly would be overturned if a new state referendum were held, DeCamillo said.
The latest Field Poll, in February, measured voter approval of gay marriage among registered California voters at 59 percent, which was the highest in 35 years of polling on the issue, while only 34 percent disapproved. In the first Field Poll on the topic, in 1977, 59 percent opposed gay marriage and 28 percent were in favor.
Nonetheless, the largest gay-rights group in the state, Equality California, remains cautious and isn't yet ready to begin a campaign to overturn Prop 8. A federal court has struck down the law, but that ruling has been appealed.
"We aren't confident that the level of support is stable enough to withstand the rigors of a referendum," said spokeswoman Rebekah Orr. "We know that people are conflicted. Their intellectual position can show up in a poll and their emotional position shows up in the voting booth."
California is among 30 states where voters have approved amendments limiting marriage to unions of one man and one woman. In Hawaii, voters passed an amendment in 1998 empowering the Legislature to ban gay marriage, which it proceeded to do. The ban remains in effect, though Hawaii lawmakers approved civil unions last year.
The other statewide vote was in Maine in 2009, when 53 percent of the voters overturned a law that would have legalized same-sex marriage.
The issue is back on Maine's ballot for Nov. 6, with voters getting another chance to approve same-sex marriage. Schubert, who is advising gay-marriage opponents in Maine, depicts it as the toughest contest for his side among the four statewide elections this fall.
In Minnesota, voters will be deciding whether to approve a gay-marriage ban similar to those in the other 30 states. In Maryland and Washington, assuming enough valid signatures are gathered by gay marriage opponents, there will be ballot measures seeking to overturn same-sex marriage laws passed by legislators this year.
However those four referendums turn out, there's widespread belief among gay rights activists and many pollsters that support for same-sex marriage will continue to grow nationwide.
"The numbers are inexorably moving in one direction," said DeCamillo. "Older folks, who are more in opposition, are dying out and younger folks are more inclined to support it. It's not rocket science."
He said support for gay marriage is surging in California among young Latinos and Asian-Americans. Nationally, according the recent Washington Post-ABC News poll, support has risen among blacks since President Barack Obama's endorsement of same-sex marriage on May 9.
Phyllis Watts, a consulting psychologist from Sacramento, Calif., has worked with several recent ballot-measure campaigns, including the failed effort to defeat Prop 8 in California and a successful drive last year to defeat an anti-abortion "personhood" measure in Mississippi.
She believes a statewide vote in favor of same-sex marriage is likely to come soon. But she suggests that any particular poll should be viewed with caution.
"People are in a fluid state around same-sex marriage. They really can feel one way one day and another way another day," she said. "I don't think the polls are able to track, with a level of nuance, what's actually occurring inside people's hearts."
David Crary can be followed on Twitter at http://twitter.com/CraryAP
- Chaffetz expected to announce he's running...
- Guatemalan mudslide death toll reaches 69,...
- Veteran who tried to stop Oregon gunman was...
- 'A terrible day' - 9 killed by gunman in...
- More police refusing to name shooters for...
- Trump defends 2nd Amendment following Oregon...
- Hatch calls shutting down government over...
- Oregon gunman was Army dropout who studied...
- Hatch calls shutting down government... 67
- Gunman opens fire at Oregon college; at... 62
- 'A terrible day' - 9 killed by gunman... 61
- Investigation: Secret Service tried to... 52
- Obama says response to shootings has... 49
- Chaffetz expected to announce he's... 48
- GOP: Planned Parenthood spends federal... 45
- Obama says fight against Islamic State... 26