Campaigns, at their most basic, are an argument over the past and the future. It seems to me that President Obama has already won the first argument. Unexpectedly, and perhaps without precedent, the nation’s weak economy has not been enough for Mitt Romney. Nor has the very real disappointment in Obama’s presidency — the performance gap — been enough. One of the reasons Romney has achieved such an historically low bounce from his convention is not only due to the shrinking impact of conventions, but because he kept trying to win an argument about the last four years.

In Tampa, Romney and Paul Ryan kept arguing that Obama is responsible for the economic mess that we are in and for the magnitude of the debt crisis. Problem is, people don’t believe it. Sure, they don’t think the president has done a good job, but their apportionment of blame doesn’t favor Romney. Asked to choose whether George W. Bush or Obama is more responsible for the bad economy, 32 percent blame Obama; 54 percent blame Bush. The president gets some credit for saving the economy from an even worse fate and for fighting against an intransigent Republican House and a cloture-proof Senate. By the way, the answer Obama’s supporters should give to the question of whether people are better off today than four years ago is: yes, better, clearly — the financial crisis is resolved, new jobs are being created instead of being destroyed — but certainly not good enough.

And this leads to the second argument: over the future. Here, too, Romney and Ryan have done Obama a favor because their ideas for the future — more tax cuts, entitlement cuts, less regulation — are part of a discredited past. But Barack Obama cannot win the election unless he engages on the future. When he leaves Charlotte, Americans need a much clearer idea of what his second term will be about. And they need some greater confidence that he will be able to navigate the hostile environment that is Washington. Without those two pillars, Obama could win the argument but lose the election.