Obama has won reelection and talk turns to whether he really has a mandate. But presidents being able to obtain a clear mandate is a subjective myth propagated by pundits, presidents, supporters and detractors alike. The mandate is neither enshrined in law nor acknowledged cohesively in spirit. So no matter how much Obama has won by those who oppose him and those he tries to work across the aisle with will not accept any mandate he articulates. Those very same people will also feel that they were reelected with mandates of their own to pursue their respective agendas.
It is beginning to look like Obama obtained 50.79% of the popular vote over Mitt Romney’s 47.65% with a margin of victory of 3.14% over three million votes. This makes him the third candidate since FDR to win the majority of the popular vote in consecutive elections. The Democrats themselves also gained seats in both the House and Senate. As for the Electoral College, it was a landslide with Obama getting 332 votes to Romney’s 206. Democrats and supporters will say this all adds up to a mandate. A mandate to let them do whatever is needed at the time whether it is letting the Bush tax cuts expire or pursuing immigration reform. The beauty of a broad and vague campaign (the kind both Obama and Romney ran) is that now Democrats can say they have a mandate to do anything that falls under the broad banner of moving “forward.”
Republicans and their supporters will of course argue that Obama has no mandate, claiming that Obama's campaign was too vague policy wise and too negative in general. For politicians and pundits whether or not the person who won the election has a mandate depends on whether it's the person you wanted to have won. Besides, these days for every president with a mandate there is a congressman or senator of the opposite party that thinks they were voted in with just as valid of a mandate to do things their way.
The mandate is a fiction. Every politician is going to do whatever he or she can to get things done their way, mandate or no mandate. Politics is about those fights, compromises, and deals. No opposition congress member would ever say “well, I totally disagree with the president and his policies, but he won by enough to have a mandate so I have to vote for them.” The mandate is not and never has been real. The only thing that is real is the messy business of politics.