What's wrong with Paul Krugman's argument?

Let's peek behind the veil of "NY Times Select" today and review the first two paragraphs of Paul Krugman's column:

In October 2003, the nonpartisan Program on International Policy Attitudes published a study titled “Misperceptions, the media and the Iraq war.” It found that 60 percent of Americans believed at least one of the following: clear evidence had been found of links between Iraq and Al Qaeda; W.M.D. had been found in Iraq; world public opinion favored the U.S. going to war with Iraq.

The prevalence of these misperceptions, however, depended crucially on where people got their news. Only 23 percent of those who got their information mainly from PBS or NPR believed any of these untrue things, but the number was 80 percent among those relying primarily on Fox News. In particular, two-thirds of Fox devotees believed that the U.S. had “found clear evidence in Iraq that Saddam Hussein was working closely with the Al Qaeda terrorist organization.”

Can you spot the gaping, glaring, blindingly obvious logical fallacy buried in this argument?

Ah yes, it's our old friend, the causation-correlation fallacy. Krugman is assuming here that people believe these misperpections about the Iraq war because they listen to FOX. The problem is that it's equally possible -- I would even say "overwhelmingly likely" -- that the people who watch FOX already had misperceptions about the war, and FOX was simply catering to them via it's own special brand of jingoist talking dipshits. Similarly, did NPR succesfully persuade its listeners that there were no WMDS -- or were NPR listeners already skeptical of their claims?

This is an elementary mistake in logic. So why does Paul Krugman think he can fool us? (Because it fits into his larger point about the danger of Rupert Murdoch buying the Wall Street Journal.)