Many years ago, political scientists came up with a theory that elites lead public opinion. And on some issues, they clearly do. But on some issues, they don’t. Two examples of the latter phenomenon are conspicuous at a time when Barack Obama enjoys the approval of more than 60 percent of Americans and Democrats have won thumping majorities in two elections in a row. One is global warming. The other is gun control. On both issues, the elites of academe, the media and big business have been solidly on one side for years. But on both, the American public has been moving in the other direction.