WASHINGTON – A Republican senator’s embrace 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 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.