Who would have thought that President Obama's most dangerous critic at this point would be a left-leaning college professor? With the Republicans struggling to craft a coherent message on the economy, New York Times columnist Paul Krugman has filled the void as the voice of the opposition, leading an assault on Timothy Geithner's economic plan and deriding Obama's stimulus efforts as insufficiently small. As one of the few prominent economists who warned ahead of time of the impending economic crisis, his words carry far greater weight that most commentators. "No one has as big a megaphone as I have," Krugman told Newsweek in a front-page profile this week. "Aside from the world going to hell, it's great."