While a majority of Democrats and independent voters support same-sex marriage, a majority of Republicans do not — but among young Republicans, 56 percent join Democrats and independents in supporting the issue.

Image Richard Tisei, far left, is one of three gay Republicans running for Congress this year who are featuring their significant others in campaign ads. Mr. Tisei’s ad features his husband, Bernie Starr, at their wedding reception this year. Credit... Richard Tisei for Congress

There are currently six gay members of Congress — five in the House and one in the Senate — and one bisexual, Representative Krysten Sinema of Arizona; all are Democrats. The last openly gay Republican to serve in Congress was Representative Jim Kolbe of Arizona, who retired in 2006; no Republican has been openly gay when first elected to Congress. (Mr. Kolbe revealed his sexuality after joining the House in 1985.)

On Thursday, the National Organization for Marriage, which supports traditional marriage between a man and a woman, held its second annual “March for Marriage” at the Capitol in Washington. “It is a losing issue at the ballot box,” said Brian S. Brown, the group’s president, “and you’re going to see that if any Republican presidential candidate were to endorse same-sex marriage, I can guarantee you they’re not going to win the Republican primary.”

Mr. DeMaio, Mr. Innis and Mr. Tisei have not broadcast any television commercials with their partners or husbands yet, although Mr. DeMaio plans to show a shorter version of his online ad on television, and the other two campaigns said they would not rule out a television buy.

“The airwaves are loaded with candidate wives and kids,” said Elizabeth Wilner, the senior vice president for politics of Kantar Media Ad Intelligence, which monitors political advertising. “These tentative off-air steps, while landmark, show just how loaded the most ‘101’ ad of a campaign, the bio ad, can be for a gay candidate.”

Nonetheless, the candidates say they need to be part of the future of the Republican Party if it wants to survive, as public opinion and Supreme Court decisions seem to be becoming more open to gay rights. “My brand of Republicanism is that the government should get off your back, out of your wallet and away from the bedroom,” Mr. Tisei said. “For the Republican Party, that philosophy is really key for us to expand our base and become more inclusive about bringing people in.”