President Obama’s endorsement of gay marriage has already excited donors and the Democratic base. But will it hurt Democrats down-ballot?

President Barack Obama waves as he leaves the stage after speaking at a fundraising event Thursday, May 10, 2012, in Seattle. (Elaine Thompson/Associated Press)

It’s possible.

Combined data from Washington Post-ABC News polls do show that while the country as a whole tilts in favor of gay marriage, voters in some key swing states oppose it.

In Indiana, Missouri, Montana, Nebraska, North Dakota, Virginia — competitive states where Democratic candidates break from Obama — registered voters break against gay marriage 54 percent to 43 percent.

Indiana in particular shows far higher rates of opposition to gay marriage than nationally. In GfK MRI surveys, 57 percent of Indiana adults “completely agree” that marriage should be legal only when it’s between a man and a woman, well above the U.S. average of 45 percent.

In the Post-ABC data, enthusiasm also favors the opponents: 45 percent of voters in the five states are strongly against gay marriage while only 26 percent are strongly for it. That suggests turnout at the margins could be affected by the president’s position, with socially conservative voters inspired to come to the polls by their gay marriage opposition.

All that suggests a potential problem. But it seems unlikely that gay marriage will be much of a wedge issue in Senate races this cycle.

Seven of the 11 Democratic nominees or likely nominees running for open seats this cycle already support gay marriage. Of those, four are running in swing states — Rep. Tammy Baldwin in Wisconsin, Rep. Shelley Berkley in Nevada, Rep. Martin Heinrich in New Mexico, and former Sen. Bob Kerrey in Nebraska. (Rep. Mazie Hirono in Hawaii, Rep. Chris Murphy in Connecticut and Harvard Law Professor Elizabeth Warren in Massachusetts are the others.) In those races, nothing has changed, although Obama’s endorsement might elevate the issue a bit.

In other states, Democratic Senate candidates have taken pains to distance themselves from the president. Rep. Joe Donnelly in Indiana said Thursday that he stands by his belief that marriage is between a man and a woman. Sens. Claire McCaskill in Missouri, Joe Manchin in West Virginia and Jon Tester in Montana put out statements making clear that their opposition had not changed. Former governor Tim Kaine in Virginia says he believes in “the legal equality of relationships” but has stopped short of endorsing gay marriage.

Those candidates are in a somewhat awkward position, but Democrats argue that voters who would change sides based on the president’s support for gay marriage are lost to them already. (They also argue that in Massachusetts, where Republican Sen. Scott Brown opposes gay marriage, the issue will help Democrats.)

National Republicans have not attacked Obama on the issue, instead labelling it a distraction from the economy.

David Winston, a Republican pollster who advises GOP congressional leaders, suggested that the same dynamic is at play down the ballot.

“Any day that Democrats don’t have the issue be jobs and the economy is a day they’re doing better,” he said. “That’s probably a good day for all Democratic candidates.”

It was an echo of what House Speaker John Boehner (R-Ohio) said a day earlier: “The president can talk about it all he wants; I am going to stay focused on what the American people want us to stay focused on, and that’s jobs.”

Dave Barie in the Post’s research and analytics department contributed to this report.