Another constraint on Obama is that he cannot really claim a mandate. First, winning 53 percent of the popular vote is not exactly a landslide. Also, those who voted for him did so for differing reasons. Some voted for him because of his Iraq policy. For some it was the financial meltdown. Some people had a nebulous desire for “change” that had no policy content. Some Obama voters, in fact, didn't really vote for Obama at all as much as against George Bush and the Republicans [Jon Schaff, "Constraints on President Obama," South Dakota Politics, 2008.11.25].
Just for fun, let's take a trip in the Internet Wayback Machine, to a Nov. 23, 2004 post from SDP founder Jason Van Beek, who cited the following from Lyn Nofziger:
In reality, the president can thank Republican gains in the Senate and House for giving credibility to his claims of a mandate. The defeat of the Senate minority leader, Tom Daschle of South Dakota, was, next to Mr. Bush's own win, the Republicans' most significant victory.
The GOP gained four Senate seats in 2004. So far in 2008, Dems have gained seven.
In fairness, Nofziger's own thesis was that claims of a Bush mandate in 2004 were hot air. Obama won bigger than Bush by most counts (exception: Bush 2004 pulled 31 states; Obama 2008 pulled 28 plus DC), but do we call it a mandate? Washington Post's Chris Cillizza says you betcha... but what does Chris Cillizza know—he thought Badlands Blue was South Dakota's best political blog. (Chris—get out and read more!)
Maybe the mandate is defined not so much by the vote total as by the situation. In 2004, Bush claimed a mandate, but neither he nor the rest of the country seemed to know what to do with it. In 2008, everybody's attention is focused squarely on one overarching issue:
Even lots of folks who didn't vote for Obama want him to do something about this economy. Even if Obama's specific policy responses won't win everyone's support, that almost universal desire for action and solutions constitutes the closest thing to a mandate we've had since 1980.