Julian Zelizer: Many Wild Cards Could Swing the 2012 Presidential Race

Julian Zelizer is a professor of history and public affairs at Princeton University. He is the author of "Jimmy Carter" (Times Books) and author of the book "Governing America" (Princeton University Press).

Princeton, New Jersey (CNN) -- The outcome of the election of 2012 is becoming even tougher to predict, since there are many political landmines facing both parties.

President Barack Obama has enjoyed a resurgence in his political standing, with polls showing him ahead of the GOP rivals in hypothetical matchups for the general election. Recent statistics showing an improving economy have bolstered the president's position, while his budget proposal and increasingly populist rhetoric have generated some excitement within the base of the Democratic Party.

On the Republican side, Mitt Romney remains the front-runner, though barely, still enjoying the kind of edge in campaign contributions that is essential to victory....

For Obama, the biggest threat is Europe. Even though leaders have put bailout plans in place and nations have started to grapple with their budget problems, the governments of Greece, Italy and other nations remain fiscally unstable. If any of these countries should default, they could trigger the kind of financial chaos in world markets that could doom Obama's re-election bid....