Political scientists understand that economic conditions play a massive role in shaping people's opinions about their political leaders. Economic conditions are not the only factor -- other things, like wars or scandals can play a huge role, especially over a short period of time. But any understanding of a president's popularity must begin with the state of the economy.

John Judis made this case persuasively last fall. A couple of his graphs from John's article tell the tale. Here's Ronald Reagan's first term:

And here's Bill Clinton's second term:

Again, unemployment doesn't tell you everything, but it tells you a lot.

This brings us to Barack Obama. Any self-respecting political scientist will tell you that the biggest economic crisis since the Great Depression is affecting the public's disposition toward the party in power. We can argue about whether that factor entirely accounts for the public mood, or accounts for just a great portion. Indisputably, it's an enormous factor.

I have noticed a recurring theme in Republican commentary has been to ignore the economy in assessing the public's sour mood toward the party in power, and to assert that disapproval of the Democrats is entirely a function of public revulsion at the liberal agenda. One could make a case that the Democrats have politically overreached. I disagree. But to characterize the backlash as driven entirely by concerns about policy, without mentioning the pull of an economic crisis that began before Obama took office, is not an argument that any political scientist, or even a candid pollster or political adviser, would take seriously. It's pure propaganda.

This recent piece of gloating by former Bush administration Minister of Propaganda Peter Wehner offers a nice example of the genre. It's filled with giddy recitation of Democrats' troubles, topped with the triumphant conclusion, "Liberalism’s 'sort-of God' is crashing before our eyes. So, it seems, is his party. It is really quite an extraordinary thing to witness."

I've decided to name this genre of propaganda "The Wehner Fallacy," mainly because Wehner has offered up the most recent example of it, not to mention an especially obnoxious one. But the phenomenon is not limited to Wehner. I'm planning to keep track of it as it happens. Please send in examples if you see them.