Once Romney becomes nominee, expect the gap to widen.
On the average, an incumbent Governor or Senator adds roughly 6% to his approval rating before the campaign season begins to get a likely share of the vote in a binary election. (This rules out contests in which there is a strong Third Party candidate who mucks the model up). Such implies average competence of an incumbent as a politician and campaigner from then on, and opponents of average quality.
Breaking scandals? Voters usually find the incumbent aloof and inaccessible, usually resulting in a low approval rating before the campaign.
Opponents can carp all that they want while they challenge the details of the incumbent's record -- and the incumbent can't please everyone. Every incumbent politician is obliged to take sides on issues that displease at least 45% of the public -- or else dodge the issue and fail to do the job. Our elected officials very rarely vote on "rainbows and sunshine" but instead vote between irreconcilable options.
Once the campaign begins, most incumbents show why they were elected to the office that they hold. If those were the wrong reasons this time but the right ones the previous time, then the incumbent probably loses -- which shows up before the campaign season anyway. We already see that with many current Representatives. Sure, it's possible to ride a wave, but a wise surfer knows when to abandon the surfboard.
The high disapproval rating shows people who also disapprove of the eventual Republican nominee. So how does one vote when one likes neither? One either can't decide and somehow doesn't vote, votes based upon some random event (like a coin toss) -- and that evens out over a large number of people, or perhaps wastes one's vote on an independent or third-Party nominee.
At this point I would have to give President Obama a slightly-better-than-average chance of winning Arizona. Things still have to break right for him. Of course he loses the state if he doesn't campaign there. There will be an open Senate seat.
But I can say this: President Obama is an above-average campaigner; he has an agenda attractive to slightly more than half the US population; any one of the remaining Republican challengers looks far short of Ronald Reagan as a challenger. If he were a below-average campaigner and faced a strong challenger he would lose all but three of the states on the list (probably three of CO, IA, NH, and PA)... and we would see that already. He would have an approval rating around 40% and Democrats would say "This and this and this and this and this must happen and then the President would have a chance to be re-elected". That's like saying that if a bunch of things go right someone with a 2.9 high school GPA and mediocre college-board scores in a public high could get a chance to attend Harvard.
