A new Washington Post/ABC News poll shows that a solid 58 percent of Americans support legalizing same-sex marriage, compared with 36 percent who believe it should be illegal. The findings represent nothing less than a stunning collapse of opposition to gay marriage: As recently as 2003, the numbers were reversed, with 37 percent favoring gay marriage, and 55 percent opposing.

The polls comes on the same day that former Secretary of State Hillary Clinton formally announced her support for same-sex marriage, and less than a week after Sen. Rob Portman of Ohio, a Republican, said he had switched his position on the issue after he learned that his son was gay. According to the Post, "Americans increasingly see homosexuality not as a choice but as a way some people are."

Surprisingly, nearly two-thirds of respondents said the legality of gay marriage should be decided on constitutional grounds, rather than leaving it up to individual states to decide. In announcing his support for gay marriage last year, President Obama said he preferred the latter, perhaps an indication that his historic announcement has already fallen behind the pace of popular opinion.

Support for gay marriage is stratospherically high among young adults, with a full 81 percent of respondents between the ages of 18 and 29 in favor. That is just the latest warning signal for the Republican Party, which could be in danger of alienating a whole generation of voters over its opposition to the issue. Just today, the Republican National Committee released a rebranding plan that called on the GOP to show more flexibility on the issue. "Already, there is a generational difference within the conservative movement about issues involving the treatment and the rights of gays," the report reads, "and for many younger voters, these issues are a gateway into whether the Party is a place they want to be."

A majority of Republicans — 59 percent — currently believe gay marriage should be illegal. However, that is down from 72 percent in 2004.