CHICAGO -- There are just 15 days remaining before the Iowa caucus. One of the things that make it unusual is the fact that you can actually win the popular vote and still come in second in Iowa.

Political Editor Carol Marin answered that question and others on the road to Iowa.

In the West Loop on Wednesday, the phones were humming all the way from Chicago to Keokuck and beyond.

The Obama volunteer headquarters on West Adams is where everyone has come with one purpose in mind.

The latest polls out of Iowa show Sen. Barack Obama continuing to hold a slim lead among likely caucus-goers.

A Washington Post-ABC News poll put Obama's support at 33 percent. Sen. Hillary Clinton gets 29 percent, and John Edwards 20 percent.

Between 125,000 and 150,000 registered Democrats are expected to caucus Jan. 3.

And in a strange Iowa twist, it's not necessarily who gets the most votes, but the most delegates, who is declared the winner.

For instance, take a town like Iowa City, the sixth-largest city in the state.

"So, 500 persons showing up in one precinct in Iowa City actually don't have as much say as 20 people showing up in a rural precinct, in terms of electing the delegates," University of Iowa professor David Redlawsk said. "And it's primarily because it will take more people to elect a delegate in a big urban precinct."

The Washington Post poll shows candidates Joe Biden, Chris Dodd and Bill Richardson are in the single digits. But that doesn't mean their supporters won't play a role at the caucus.

Remember this word: viable. If a candidate doesn't get 15 percent of the vote in the caucus, they don't get delegates and they are considered not viable. So if Biden, Dodd or Richardson don't hit the 15 percent mark, their supporters are allowed to go and pick their second-choice candidate. According to the poll, Obama's lead would widen slightly when second-choice voters are factored in.

But Redlawsk cautioned not to read too much into voter surveys.

"There is also a get-out-the-vote factor here that is huge. That is the ability on the ground to knock on doors and bring folks to the precinct caucus' which you just can't poll for," he said.

"Is a sleeper possible?" Marin asked.

"It is possible. I mean, things can happen in the Democratic caucus, they can happen because it is all about who actually shows up that night," Redlawsk said. Tuesday night in Chicago, Clinton urged supporters to go west and campaign for her in Iowa.

Similarly on Wednesday night, Obama volunteers burned up the phone lines. Why? According to poll results, as many as one-third of Iowa voters say they could still change their minds.