Obama will also have some leeway with the Congress -- probably more than most presidents have. Yes, Bush had two houses of Congress of his party, as well, but the GOP didn't have nearly the majorities that the Democrats currently enjoy. Bill Clinton had about as many Democrats in the House in his first two years as Obama will have next year, but it was a very different Democratic Party back in 1993*. The party has largely purged its moderates (as have the Republicans).
Beyond that, aspects of this year's election may extend Obama's honeymoon period, as my fellow Klugie Greg Koger notes:
In “real change elections,” Koger observed, “a president can have continued success for two years or more.” Woodrow Wilson, Franklin Delano Roosevelt, and Lyndon Johnson are clear examples of this, and the election of Barack Obama has all the marks of being another such change election. Despite the natural tensions that exist between a president and Congress, Obama has a special opportunity for success with Republicans in such disarray after two successive election setbacks. Koger added that a president “needs to choose an agenda that can be signed into law” and “minimize intra-party conflicts.” He can do this “by putting the onus on Congress to determine when and how to pass agenda items that have salience, net political benefits for the party.”Obama will have an even easier time if the Democrats get to control 60 Senate seats. That, however, would require the Dems to take the Minnesota and Georgia races and for Lieberman to be a reliable vote. Any one of those things might be possible, but all three is a real stretch.
*Update: Some evidence. According to Keith Poole's numbers, the Democratic caucus has moved leftward since 1993. The median DW-NOMINATE ideal point for Democrats in the 103rd House (1993-94) was -.337. Last year, it was -.42. Plus, the standard deviation has shrunk in the same time period from .181 to .158. House Democrats are now more liberal and more ideologically similar to each other than they were 16 ago.