As I mentioned earlier, the recent trend has been for the Democratic candidate for president to enjoy a lead, often sizable, in summertime polls. Those leads usually vanish by November. That may or may not occur this year, but a few things to keep in mind:

–The Democratic candidate normally has a hard time cresting above 50 percent of the popular vote. In fact, the Democratic candidate has gotten more than 50.1 percent of the popular vote only once in the last 60 years (h/t John Fund). It hasn’t happened in the last 34 years.

– In contrast, Republican presidential candidates have gotten more than 50.1 percent of the popular vote 7 times in the last 60 years.

– Obama enjoys about a 2-3 point lead in daily tracking polls and is at 46 percent in the RCP average of polls. Sounds good, until you realize that 46.2% is the median percentage of the popular vote received by Democratic candidates over the last 60 years. And several Democratic candidates have enjoyed far bigger leads in July only to crater in November.

–Obviously, the popular vote doesn’t determine the outcome of elections. Obama may win electoral votes in states that typically go Republican. Yet over the last 60 years Democrats have fared even worse in the electoral vote than in popular vote. The median percentage of electoral votes received by the Democratic candidate over the last 60 years is 38.5 percent.

These points aren’t offered to show that Obama will lose in November–in addition to his current lead in the polls he has manifold advantages: expected cash superiority, a Democratic tide and a worshipful press. The point is that the media may wish to temper their irrational exuberance for an Obama coronation in the fall. Even with his advantages Obama must overcome an intrinsic Democratic weakness in national elections in order to prevail. Indeed, but for a strong third party run in 1992, it’s arguable that Democrats would’ve won only one national election in the last 34 years.

Every election cycle the media seem to forget that Democrats almost always look great in July. But it’s a long way to November.