Gay marriage still divides the party, with the conservative wing strongly opposed. But an increasing number of Republicans, now including Sen. Rob Portman of Ohio, are reversing course. Many others simply downplay the subject.

With the issue of immigration also shifting rapidly under Republicans' feet, they seem increasingly focused — and united — on one overarching goal: keeping income taxes from rising. Their solidarity on that issue is hindering President Barack Obama's efforts to make higher tax revenue part of a compromise approach to deficit spending and expensive social programs.

These trends raise the possibility that the GOP — reeling after losing the popular vote in five of the last six presidential elections -- will lessen its identity with hot-button social issues and sharpen its emphasis on tax and spending matters.

Portman announced Friday that he now supports gay marriage, linking his stand to learning that one of his sons is gay.

A former U.S. trade representative and White House budget chief, Portman is seen as one of the party's most knowledgeable and effective leaders. Mitt Romney considered him to be his running mate last year. Portman says he told Romney of his son Will's sexuality but does not believe it affected Romney's decision.

As a U.S. House member in 1996, Portman supported the Defense of Marriage Act, or DOMA. It defines marriage as between a man and a woman and bars federal recognition of same-sex marriage.

Portman's reversal makes him the only Senate Republican to openly back gay marriage.

"I have come to believe that if two people are prepared to make a lifetime commitment to love and care for each other in good times and in bad, the government shouldn't deny them the opportunity to get married," Portman wrote in an op-ed article in The Columbus Dispatch.

He said he had talked to his pastor and others, including Senate Minority Leader Mitch McConnell, R-Ky., who opposes gay marriage, and to former Vice President Dick Cheney, who supports it.

Cheney, whose younger daughter is a lesbian, became arguably the best-known Republican to embrace gay marriage with his announcement in June 2009.

Portman said his previous views on marriage were rooted in his Methodist faith.

However, he wrote, "Ultimately, for me, it came down to the Bible's overarching themes of love and compassion and my belief that we are all children of God."

Despite his party's struggles with Americans' increasing acceptance of gay rights, many GOP leaders met Portman's news with silence or a shrug.

A spokesman for House Speaker John Boehner, who shares Portman's Cincinnati background, said the senator "is a great friend and ally, and the speaker respects his position, but the speaker continues to believe that marriage is between a man and a woman."

In January, Boehner chastised the Obama administration for dropping its legal defense of the Defense of Marriage Act, which the Supreme Court is to consider this month. Boehner authorized the continued use of public funds to defend the law in courts.

Boehner's latest comments reflect the change among many mainstream Republicans, who now deal with gay marriage in largely unemotional, legalistic terms rather than emotional terms about sin and God's will.

Congress now has several openly gay members, including a senator, Wisconsin Democrat Tammy Baldwin.

At the U.S. House, which was in session Friday, several conservatives had little or nothing to say about Portman's announcement.

Gay marriage "is not the most front-burner issue," said Rep. James Lankford, R-Okla. "We still have the same legal issues we've always had with the Defense of Marriage Act," which he supports, he said.

Citing Obama's position, he said, "It's more a separation of powers issue than it is anything else." Lankford said other Republicans have supported same-sex marriage, so "this is not anything new."

In another legal matter — California's ban on same-sex marriage — all 21 state attorneys general who have signed legal briefs or letters urging the Supreme Court to uphold the law are Republican.

White House spokesman Josh Earnest said Friday: "What is clear is that we are witnessing a pretty significant sociological shift in this country."

"It's happening right before our eyes in a way that says a lot about our country, that we have a country where we prioritize equality and fairness," he said.

Obama said last year he personally supports gay marriage, a step some liberals called overdue.

Polls show that public opinions on gay rights, including same-sex marriage, have shifted perhaps more rapidly than on any other major issue in recent times. In Gallup polling last November, 53 percent of adult Americans said same-sex marriages should be granted the same status as traditional marriages, while 46 percent felt they should not be valid.

Those figures were nearly reversed two years earlier. In 1996, when Gallup first asked about gay marriages, 27 percent felt they should be valid.

Many social and religious conservatives still oppose gay marriage. Some spoke up at the Conservative Political Action Conference, which was under way Friday in suburban Washington.

Randy Smith, a technology entrepreneur from California, said Portman's decision violates key conservative principles.

"Conservative values are based on God's word," Smith said. "If he is professing to be a Christian, I'd have no part of him."

Arne Owens, a "pro-family movement" activist from Virginia, said Portman's shift "does make it harder to maintain support for traditional marriage. There's no question about that."

John Radell, head of the Faith and Freedom Coalition of Delaware, said Portman's personal situation was difficult, "but that doesn't mean you stray from your faith."

"I understand loving your son," he said. "But Sen. Portman represents more than his son."

Radell said that "without question" Portman's shift would make his political future — particularly any presidential aspirations — more difficult.

Curt Steiner, an Ohio GOP consultant who helped run Portman's first House campaign in 1993, disagreed.

"I think it's always good to be forthright with your positions," Steiner said. "Some social conservatives will disagree with Rob Portman on this issue, but they understand the life that he leads, they understand his commitment to family, and they understand his commitment to them."

The leader of a conservative group that promoted passage of a 2004 amendment in Ohio to ban gay marriage said he has heard from several people upset by Portman's stance.

"They feel betrayed," said Phil Burress, president of Citizens for Community Values. "They're not mad. They're sad and betrayed."

Ohio Republican Party Chairman Bob Bennett agreed that some Republicans are unhappy, but he said he received more phone calls Friday about the governor's budget. He said Portman has "taken a great deal of time to think it through and I certainly respect his right to make up his own mind."

Richard Socarides, who was President Bill Clinton's top adviser on gay issues, said Portman's son Will "proved once again that the most powerful political act any gay person can take is coming out." He said polls show that "people who know a gay person are far less likely to support discrimination."

Other prominent Republicans who have endorsed gay marriage include: Sen. John McCain's wife, Cindy, and daughter, Meghan; former first lady Laura Bush; former national GOP Chairman Ken Mehlman and former U.S. Solicitor General Ted Olson.

Associated Press writers Ken Thomas, Steve Peoples, Donna Cassata and Jim Kuhnhenn in Washington and Kantele Franko in Columbus, Ohio, contributed to this report. Ann Sanner reported from Ohio.