It's just one more explanation for why the Democratic nomination is so often seen as a two-person race.
But at least in Iowa, the numbers tell a different story, CBS News senior political correspondent Jeff Greenfield reports. It's a virtual three-way dead heat.
"Well, you can't count Edwards out," said Ann Selzer, who directs the Des Moines Register poll.
She points to former vice presidential nominee John Edwards' strong second place showing four years ago.
"He's been through this before and he knows what it is to surge at the end," she said.
So what is John Edwards doing? As he did for years ago, he's crisscrossing the state of Iowa arguing that he is the most electable Democrat based on who he is, where he's from, and what he's for.
Part of the argument is geographic.
"I'm the one candidate on our side who's actually won in a red state and grew up in small town rural American," Edwards said in Iowa. "And I might add, you know, as a practical matter, the last two Democrats who were elected president of the United States, they talked like this."
But he also links that working-class background to his core political argument: a frankly populist attack on corporate wealth and power.
"The power in government, in our country, has become concentrated in the few, affects every single thing that's happening," he said.
It's the theme of a new ad linking his campaign to his wife's life-threatening illness:
"And Elizabeth and I decided we're not going to quietly go away," he says in an ad. "Instead we're going to go out and fight for what it is we believe in."
Edwards end game is simple: find the Iowa Democrats who want change, convince them that change requires a fighter and not Obama's intention to be a healer.
And hope for a win here that turns a two way fight into a three-way