WASHINGTON — A Republican senator’s endorsement of gay marriage is the latest sign of soul-searching in a party struggling to adapt in a society whose demographics — and views on emotional issues — are changing fast.
Gay marriage still divides the party, with the conservative wing strongly opposed. But an increasing number of Republicans, now including Senator 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 thwarting President Obama’s efforts to find 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 US 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’s sexuality but doesn’t think it affected Romney’s decision.
As a US House member in 1996, Portman supported the Defense of Marriage Act, which 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, Republican of Kentucky, who opposes gay marriage, and former vice president Dick Cheney, who supports it.
Cheney, whose 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.