Support for same-sex marriage reaches all-time high, poll finds Seven years later, that picture has turned upside down. The change is apparent across the board, with Americans of all political stripes and age groups becoming increasingly supportive of gay marriage. Fully 81 percent of adults between the ages of 18 and 29 support such unions, and although support dips to 44 percent among those 65 and older, both of those figures are highs. Most Republicans continue to oppose same-sex marriage, but among Americans younger than 50, a slim majority of Republicans and GOP-leaning independents now support it. On Monday, there were signs that both parties" establishments were trying to catch up to this shift in beliefs. Republican leaders, performing an "autopsy" of last fall's election defeats, said they fear that the GOP's position on same-sex marriage is driving some young voters away. And among Democrats, former secretary of state Hillary Rodham Clinton appeared in a Web video to endorse legalizing same-sex marriage. "I support marriage for lesbian and gay couples," Clinton says in the video, released by the Human Rights Campaign, an advocacy group. I support it personally and as a matter of policy and law. During her presidential run in 2008, Clinton endorsed same-sex "civil unions" but not marriage. But her shift does not make her the first major potential contender for the 2016 Democratic nomination to signal support for gay marriage. In fact, it makes her the last. She follows Vice President Biden, Maryland Gov. Martin O'Malley and New York Gov. Andrew M. Cuomo. Peter Sprigg of the Family Research Council, one of the most prominent of the groups that oppose same-sex marriage, said: "I don't believe we're losing the battle. We've certainly lost some ground in public opinion. His group believes that traditional marriage - between one man and one woman - is dictated not just by civil and religious laws but by nature as the institution best suited to raising children. "Obviously, we've lost some ground in terms of the states that have" legalized same-sex marriage, Sprigg said. But he said he is optimistic: "I think we'll continue to have a lively and vigorous debate, state by state." Next week, the U.S. Supreme Court will hear arguments in two closely watched cases that are challenging legal limits on same-sex marriage. One case involves California's Proposition 8, a voter-approved measure that bars such marriages in the state. The other is a challenge to the 1996 Defense of Marriage Act. That law withholds federal recognition of same-sex marriages performed in the nine states, and the District of Columbia, where they are legal.