IT HAS now become less politically risky for Democrats to accept gay marriage than to support taxing the richest 1 percent of Americans. And that reality speaks volumes about the Democratic dilemma. On Wednesday, Senate Republicans offered a constitutional amendment banning same-sex marriage that they knew had no chance of passage. Their purpose was simple and cynical: Rally the faltering Republican hard-core base, and force a vote that they hoped would embarrass Democrats. The constitutional measure, which required 67 votes to pass, got only 49. Just one Democrat, Ben Nelson of Nebraska, supported it. Seven Republicans, including all five New...