Or so goes the idea. People remember the horrible, mindless attacks on the Clintons in the '90s, and recognize the same sort of shameless slander at work in the primaries now, and conclude: "People--right or wrong--have an irrational hatred of anything Clinton. Therefore, Hillary Clinton will not be able to become president, so Democrats should nominate Obama instead."
But as Dave Neiwert notes, "If Obama is in fact the nominee, you can bet your bottom dollar that the Clinton Rules will be applied to him as well." It's not something special about the Clintons that attracted all this vituperation, and there's nothing special about Obama that will make him immune to it.
As proof, you can read two posts from Ed Brayton today about insane right-wing attacks against Obama: one saying Obama is equivalent to Hitler; and the other that he's a communist.
Then there are all the bizarre delusions that have already become media talking points: he went to a madrassa; he's really a Muslim; he won't wear a flag lapel; he doesn't put his hand over his heart during the national anthem; and more.
And finally there are those who attack him for daring to have the middle name Hussein or a last name that rhymes with Osama.
So in short: to hell with choosing a nominee based on who elicits less of a visceral reaction from certain segments of the population right now. By the time the actual election rolls around, you'll have people who would rather kill their own mother than vote for the Democratic nominee, whoever it is, because this is what the right-wing noise machine does.