Obama's real challenge for this fall
...I think as people get to know his positions and get past the "hope and change" mantra Obama's numbers will continue to fall. It is not clear yet whether those voters in the Democrat primary who say they will not support him if he is the nominee are reflected in the current polling.
No candidate in the modern primary era has ever been elected in November after failing to win more than one of the nation's seven largest states in either its pre-convention primary or, if the state didn't hold a primary, its caucuses. That will be the case if Obama loses Pennsylvania in April. (Admittedly, no one who lost six out of seven has ever been nominated either, so perhaps Obama can make history twice.)
No Democrat who hails from north of the Mason-Dixon Line has been elected president since John Kennedy in 1960.
No candidate in the modern era has ever been elected president with a voting record that could be identified as his party's most liberal or conservative, yet the National Journal found Obama to be the most liberal senator this past year after computing his Senate voting record. (The previous closest attempts by candidates on the comparable extreme were made by the Right's Barry Goldwater in 1964 and the Left's George McGovern in 1972, and we know what happened to them.)
At this point in the election cycle -- before any fear of the unknown has set in -- challengers are often running much better against their incumbent-party opponents. In 1988, Michael Dukakis had about a 10-point lead over George Bush (the senior and then-vice-president), only to lose by around eight -- an 18-point swing.
Ditto in 2000. George Bush (the younger) had about a similar 10-point lead over Al Gore at this stage, only to see the lead shrink to nothing by Election Day.
In fact, that's been the usual pattern. In 1976, Carter led Gerald Ford by 10 points in the spring, and even McGovern in the spring of 1972 found himself running roughly even with Richard Nixon (albeit with a potential George Wallace third-party candidacy in the mix). By November, the incumbent had surged considerably in both cases.
Even in 2004, John Kerry ended up doing worse in November than he had in the spring, at least according to the CNN/Gallup poll that gave him a five-point lead in April.
The only modern exceptions to this involved Bill Clinton, in 1992, and Ronald Reagan, in 1980. In both elections, the insurgents came from behind. But both faced notably different circumstances than Obama does.
First, Clinton and Reagan got to run against unpopular incumbents. McCain is not George Bush -- no matter how much Obama may try to tie the two together.
It is clear that Osama bin laden and Zawahiri have gutted his rational for retreat from Iraq and he so far has not seemed to notice. The voters will before the election is held.
David Paul Kuhn takes a look at the polling and sees more crossover votes headed to McCain than Obama. That is a necessity for McCain since there are apparently more Democrats than Republicans.