Obama will be a lame-duck President with an energized opposition in both the House and Senate. Hopefully we will put enough conservative Republicans in who will block him at every turn. He won't get away with much.
Romney, on the other hand, will be the head of the GOP. Republicans in the House and Senate will be very disinclined to counter their Party's boss. Romney will be a "place-holder" President who will govern like he did in Massachusetts - in other words, he will be a liberal statist. In addition, the DemocRATs will blame Romney for every economic time-bomb that Obama has laid. Minutes after Romney is sworn in, Chuck Schumer (the head of the inauguration committe, BTW), will rush to the cameras and declare "It's Romney's economy now!" With Romney at the helm, the DemocRATs will come roaring back to power in 2014 and 2016 with the message "We TOLD YOU SO!"
BTW, how'd you like to see Obama run against President Romney in 2016?
Look, I hate. Myth, BUT he has backed the Ryan budget no?