Democrats face a difficult challenge in responding to the question, a well-worn but still devastating attack for any incumbent.

Sometimes reams and reams of data, and brilliant young staffers ready to decipher them, aren't enough to protect a campaign from an ambush. So it was this weekend, when Obama surrogates were asked whether Americans were better off than they were four years ago.

It's tough to say which is more surprising: that Republicans hadn't pulled out the question -- immortalized by Ronald Reagan in 1980 -- sooner, or that Democrats didn't have an answer ready. For example, Democratic attack dog and rumored 2016 contender Martin O'Malley, the governor of Maryland, said no, then quickly reversed himself (his answer blamed George W. Bush for the status quo ante, but it was the no that got the attention). Jill Lawrence of National Journal has a great piece about how Democrats flubbed the question, but after a mad scramble, their answer can basically be summed up with this chart. You've probably seen variations on it before.

It's not accident that the chart uses only private-sector employment. Government jobs are shrinking quickly -- the government has fewer employees than it has for 45 years, and job losses in the public sector have been a consistent drag on the unemployment rate.

The strong and weak suits of this chart aren't hard to pick out. Even with relatively weak results through the spring and early summer of this year, it's clear that jobs have gone a long way toward recovery during Obama's term in office, and are headed in the right direction. Keep him around, Democrats say, and things will continue to get better -- even if it's not as fast as you'd like. Switch horses and things will get worse, they warn.

But of course that's not the way the question is posed, and it's not clear how many voters think that way. While there were storm clouds on the horizon, it's important to remember that the day often used as shorthand for the economic collapse, September 15, 2008, was after this point in the campaign, and not long before the election. Four years ago, most voters didn't anticipate the harrowing recession that was to come. And there's a good chance they're not better off than four years ago. Median family net worth, for example, is down to early-1990s levels. Is job creation better than it was four years ago? Sure. But people react to personal experience more than abstract statistics. Even if the country is better off -- and by just about every economic metric, things are headed in the right direction -- doesn't mean you feel you are.

That's why you can expect to hear this debate repeated over and over in the next 63 days. The Republicans know it's potent, and the Democrats know they have to walk a difficult line -- they have to explain a somewhat elaborate policy point, but can't come across as aloof to voter suffering. Luckily for them, voters still blame Bush more than Obama for the state of things. And that's why you can expect to hear his name repeated over and over at the Democratic convention and over the next 63 days too.