Bill McGurn in the Wall Street Journal:

When Barack Obama was campaigning for president in 2008, he declared that marriage is between a man and a woman. For the most part, his position was treated as a nonissue.

Now Rick Santorum is campaigning for president. He too says that marriage is between a man and a woman. What a different reaction he gets.

There's no mystery why. Mr. Santorum is attacked because everyone understands that he means what he says.

President Obama, by contrast, gets a pass because everyone understands—nudge nudge, wink wink—that he's not telling the truth. The press understands that this is just one of those things a Democratic candidate has to say so he doesn't rile up the great unwashed.

It's arguably the most glaring double standard in American life today. It helps explain why candidates with social views that are fairly conventional among ordinary Americans—the citizens of 31 states including California have rejected same-sex marriage when put to a vote—find themselves depicted as extreme.