Carter had gone through the critical 44% mark (incumbents have about a 50% chance of re-election at that point, and the chance rises to nearly 100% at 50% approval and falls to near zero at 40% approval) early in March. He would never recover. He slipped below 40% late in April. He tied with Reagan late in May... and we know what sort of campaigner Reagan was. By July his approval rating was in the 20s.
Incumbents whose approval ratings are in the 30s before the campaign season begins usually do not run for re-election. Carter started out reasonably popular and became unpopular. He recovered some, but far from enough. Before the debates he was about 5% away from Reagan, which might have been good for about a 52-48 split of the popular vote. Instead he faltered and his approval went back to the mid-30s.
He added about 6% to his late approval rating to get to his vote share of 41%, which is poor for an incumbent and close to the floor for results for the person who gets the second-largest number of popular votes (I do not include the 1912, 1968, or 1992 because of strong third-Party or independent challengers).
I have frequently suspected that except in a late-campaign collapse (breaking scandal? military debacle?) in what otherwise is until then a close election, the undecided tend to go ineffectively toward the eventual loser. Carter missed the 38% floor for a challenger facing a strong incumbent and the 39% floor for a failed incumbent facing a strong challenger, but not by much.
Carter was one of the more forgettable Presidents that we had in the 20th century -- one with few achievements and, unlike the successful incumbent he ran from his record and had to make fresh promises.
The Obama-Romney contest has been remarkably stable for most of the summer. The incumbent President has had approval ratings ranging from the mid-40s to the low 50s, and Mitt Romney has almost always lagged him. There has been no Obama collapse, and there probably won;t be one. Like previous incumbents successful in winning re-election, and much unlike Carter, the President is running on his record.
Carter was not devoid of accomplishments. He brokered the Camp David Accords and got the Panama Canal Treaty ratified. The latter, however, was unpopular, and the former lost luster in the wake of the Hostage Crisis in Iran. Carter was nowhere near as incompetant as he has been portrayed.
Carter lost because (A) his political party did not like him, and (B) he was thrust into an unprecedented foreign crisis that made him look impotent. Carter's handling of the Hostage Crisis was, IMO, proper and prudent, but there was a large constituency among his own Southern base, and in the country, that wanted a far, far more aggressive response. He also lost because he was perceived as impotent in the face of record inflation; this, too, was an unprecedented situation that was not Carter's fault. Had Carter not been challenged in a primary, and had John Anderson not run as an independent, I believe that Carter would have prevailed against Reagan, albeit by a narrow margin. Carter was not a great President, but he was not a failure; he was not James Buchanan or Franklin Pierce.
