Julian Zelizer is a professor of history and public affairs at Princeton University. He is the author of "Jimmy Carter" and of the new book "Governing America."

When Washington gets back to work, the situation will be difficult. President Obama won a sound re-election victory, doing very well in the Electoral College and winning the popular vote by more than 3 million votes. He trounced Mitt Romney in almost all the battleground states and he will return with a larger and more energized Senate majority.

Yet President Obama likely understands that elections don't remake the political system. The parties remain as polarized as ever, and the political process will be as difficult as it has been since the first day he took office. Republicans retained control of the House, where they can make it hard for the president to move his agenda forward and can place immense pressure on him to curtail spending.

While Democrats control the Senate, with 54 votes, Republicans control the tools of the Senate minority -- namely the filibuster, which requires 60 votes to pass any major piece of legislation. Exit polls showed that the public is not satisfied with the status quo, many voters opposed the idea of an activist government to solve problems, and President Obama struggled with some key constituencies, including older and suburban voters....