DENVER (AP) — Not too long ago, Republicans used gay marriage as a tool to drive Election Day turnout. But as public opinion on the issue has turned and U.S. courts strike down same-sex marriage bans, gay rights is evolving into a wedge issue for Democrats to wield.

Gay marriage, supported by less than one-third of Americans in 2004, is now supported by a solid majority in recent polls, with approval highest among younger voters. Some Republicans believe that mounting public support represents a danger to their party. With November midterm elections approaching, they are scrambling to prevent Democrats from using the issue of gay rights in the same way some in their own party did for years.

"They want to bait Republicans into talking about the issue in a way that ties them to a negative, national Republican brand," said Kevin Madden, a Republican strategist who hasn't taken a position on gay marriage.

Consider Pennsylvania, where Democrats have lambasted Republican Gov. Tom Corbett for comparing gay marriage to incest. Facing a tough re-election campaign, Corbett decided this week not to appeal a federal court ruling striking down the state's ban of gay marriage.

Or Colorado, where Democratic Sen. Mark Udall is hitting his Republican challenger for casting votes that denied gay people protection from discrimination. In Arizona, Democrats plan to hammer Republican legislators who passed a law allowing businesses to refuse to serve gays for religious reasons.

At stake in November is control of the Senate, with the Republican Party hoping to pick up the six seats it needs to take the majority from the Democrats. The Republicans are widely expected to retain control of the House of Representatives, where they have already wielded their majority to stymie President Barack Obama's legislative agenda.

Looking farther ahead, Richard Socarides, an activist who was former President Bill Clinton's adviser on gay rights, said the political shift on gay marriage will be even more pronounced "by the time we get to the (presidential) election in 2016."

That election will arrive 20 years after Republicans in Congress passed the Defense of Marriage Act, which prohibited federal recognition of same-sex marriage. Clinton signed the bill defensively, worried the Republicans would use it as a campaign issue, Socarides said. Republican activists put anti-gay marriage initiatives on the ballot in 11 states in 2004, helping President George W. Bush win re-election with the support of conservative religious voters motivated to turn out to support the bans.

Connie Mackey, head of the conservative Family Research Council's Political Action Committee, said that's still a solid strategy. Voters still oppose gay marriage, she argued, and Republicans should not let themselves get tricked by overconfident Democrats.

Nevada Republicans dropped their opposition to gay marriage last month from the state party's platform, and a national campaign is underway to remove such language from the national party platform in 2016. Major Republican donors have formed a coalition to push the party to become more gay-friendly.

That shift broke into the open in Arizona earlier this year after social conservatives pushed legislation allowing businesses to refuse service to gays and lesbians through the Republican-controlled Statehouse. An outcry from business organizations and national Republicans led Republican Gov. Jan Brewer to veto the measure, but the issue is likely to figure in at least two of the state's competitive congressional races where Democrats are defending seats, as well as the governor's race.

The politics of gay rights have changed perhaps most dramatically in Colorado. In 1992, voters passed a law prohibiting any city or county from protecting gays and lesbians under their laws against discrimination. That measure was eventually struck down by the U.S. Supreme Court, but voters went on to ban same-sex marriage in 2006.

Those actions inspired several major donors to invest in expanding the state's Democratic party. At the same time, an influx of younger voters moved to the state from the coasts. A decade-long winning streak followed for Democrats at the top of the ticket.

Democratic Sen. Michael Bennet narrowly defeated a Republican challenge in 2010 after the Republican candidate compared homosexuality to alcoholism. The next year, Democratic Gov. John Hickenlooper shamed Republicans in control of the state House for refusing to grant gay couples civil unions. The Republicans lost control of the chamber in 2012, and Hickenlooper signed a civil unions bill last year.

Seeking re-election this year against Republican Rep. Cory Gardner, Udall has highlighted his opponent's support as a state lawmaker for laws barring adoption by gay parents and opposition to adding protections for gay people to nondiscrimination clauses.

Gardner replied in a statement that he does not believe "anyone should be discriminated against." The issue, Gardner added, has no place in the campaign.

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