Sweet column: Rep. Jesse Jackson Jr. stumps for Obama. "All we got to do is believe," Jackson Jr. says. Clinton, Obama fight for Des Moines black vote

DES MOINES — Think of the Iowa Democratic presidential caucus as a contest of Olympians when it comes to the three front-runners, John Edwards, Barack Obama and Hillary Rodham Clinton.

They are all running their personal best. But Thursday night, only one will come in first, and every poll shows it is too close to call.

These Olympians have field and marketing organizations that have crunched data to death to pinpoint and turn out their likely supporters at these very peculiar public exercises of democracy called Democratic caucuses.

The battle is on the ground and in the air — Iowa television is saturated with Democratic and GOP ads.

That allies of the cash-strapped Edwards are paying for spots helping him has increasingly become an issue for Obama, as the two battle for the same change-oriented, anti-Clinton, undecided voter. Edwards is on the uptick, some surveys suggest, with the race essentially a tie.

Edwards was on the defensive over those ads when pressed Sunday why he couldn’t — as a candidate running against corporate and special-interest money in politics — do more to tell his friends to stop.

His friends bankrolling the pro-Edwards ads include labor unions and a woman in her mid-90s, an heir to the Mellon fortune who donated $495,000 to one of those independent groups bolstering Edwards’ candidacy, with the help of her lawyer, a long-time Edwards booster.

“I don’t have control over them,” Edwards told Bob Schieffer, host of CBS’ “Face the Nation.” Schieffer disagreed.

Meanwhile, on NBC’s “Meet the Press,” host Tim Russert was grilling Obama over a debatable claim in one of his television spots that his health insurance plan will “cover everyone.”

Clinton and Edwards have health insurance plans with mandates. Obama’s does not — his relies more on market forces and government bullying to lower the costs of insurance. It has been a big issue.

Obama sidestepped whether his spot was a stretch. He said that under his plan, if people waited to buy insurance until they got sick, they should pay a penalty.

On ABC’s “This Week with George Stephanopoulos,” Clinton was lowering expectations in case she stumbles in Iowa. She’s in the race for the “long term,” she said.

After the shows, Edwards, Clinton and Obama barnstormed through Iowa.

The Obama and Clinton campaigns worked to crank up black voter turnout in Des Moines. Clinton visited an African-American church with daughter Chelsea. Both teams dispatched African-American surrogates to black churches.

At Union Baptist Church, Rep. Jesse Jackson Jr. (D-Ill.) delivered a stem-winder for Obama.

“It is real easy for me to come to Iowa and say we can win this little ol’ state. And we can win New Hampshire and we can win South Carolina. We can elect us a president. All we got to do is believe. All we got to do is show up on time and caucus with someone,” said Jackson.

I’m writing this at an Obama rally, in the gym at the Nathan Weeks Middle School here, in a delegate-rich part of Polk County. The precincts around here are supposedly Clinton turf. The place is packed as Obama is doing his stump speech for the fourth time today.

Earlier, I went to a rally for Edwards at another school here, and the hall was full.

Today, the front-runners will campaign up to and including New Year’s Eve. This morning, Obama campaign manager David Plouffe will hold a conference call to assess the campaign, no matter the Iowa outcome.

“Seven days from now, we’ll be at a rally in New Hampshire,” Plouffe said as we talked in the gym. New Hampshire votes Jan. 8.