As a candidate four years ago, Michigan Gov. Rick Snyder defined marriage as "between a man and a woman.'' This week, after a court opened the door to gay marriage in his state, he declined to offer an opinion. Social issues, the Republican governor said, are a distraction.

It was one of many signs in recent weeks that the Republican Party's opposition to gay marriage, long a bedrock principle, is coming under new strains. Increasingly, prominent Republicans are softening their tone or backing gay marriage outright.

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