There is an even more telling statistic in the recent Los Angeles Times poll. In that poll, 13 percent of likely Democratic caucus voters in Iowa said that if Obama were the nominee in the fall, they would not be willing to vote for him. That's a higher percentage than any of the other candidates. I suspect it indicates the reluctance of white voters to back him. And one presumes that if what were sampled were Democrats who planned to vote in November, the percentage might be higher.
John does point out, however, that...
In the Los Angeles Times poll, 18 percent of the independents who plan to vote in the Iowa Democratic caucus say they would not vote for Clinton in the fall.
What he leaves out is that only 4 percent of independents say they would not vote for Obama, a 14-point difference. Moreover, he doesn't mention the Democratic number for Clinton--it's 9 percent (and thus only a 4 percent difference with Obama). It's also worth pointing out that this LAT poll was the most pro-Clinton poll of the last month.
The irony of the Clinton campaign's attack on the DMR poll is that their argument is an implicit acknowledgement that Obama would be a stronger general election candidate.