The 2006 campaign that Dems ran was to run against Bush, not as much for something. Then when they won, they said that win was tantamount to America adopting their agenda, which wasn’t true.
Obama and Romney are both trying something similar: run against your opponents, keep the focus on them, and avoid running for something (or on your record) if at all possible.
Not saying it won’t happen, but Obama doesn’t have an opponent yet. So far everything I’ve seen is just Obama playing the race card by proxy, against any attempt to even find someone to oppose him.