With the Iowa caucus now just two days away, a new poll from the Des Moines Register suggests that Democrat Barack Obama and Republican Mike Huckabee are maintaining small leads. But while Thursday's vote promises to be a nail-biter for both parties, an even more compelling story line may be whether the result catapults the winners to victories in upcoming primary contests. The question on Friday becomes who, if anyone, will benefit from the "Iowa Effect."

The Iowa Effect, in a nutshell, is the complete upending of the predicted presidential primary landscape by a candidate's unexpected performance in the nation's first caucus. Riding a wave of adoring press coverage by a media eager to hype the tale of the underdog, the perceived winner in Iowa sweeps through New Hampshire and subsequent primary states to take (or at least seriously challenge for) the party's nomination.

Just ask Gary Hart. In December 1983, I joined Hart's Democratic presidential campaign in New Hampshire. At that time, the Colorado Senator polled at 2% nationally and a somewhat more respectable 5% in New Hampshire, well behind the media's chosen front-runners Walter Mondale and John Glenn. Thanks to an experienced team and ground-breaking grassroots mobilization, by mid-February Hart moved into a distant second place behind Mondale. The day before the Iowa caucus and eight days before the New Hampshire primary, Hart trailed Mondale by roughly 35% to 15%.

Which is when Iowa changed everything. Sure enough, Mondale ran away with the 1984 Iowa caucus, 49% to 16%. But it was Gary Hart who finished a shocking second. (John Glenn's campaign imploded after his dismal fifth place showing.) That same night, Hart declared the nomination a two-man race and confided to an aide that his second-place showing meant he would be the next president of the United States.

Hart's boundless optimism was based on the media transformation and the tectonic momentum shift he knew would result for his stunning Iowa performance. The next day in New Hampshire, our usual press van of four reporters was replaced by two busloads of media from around the world. A week later, Gary Hart manufactured a 30% turn-around and won the New Hampshire primary by 10 points. The Iowa Effect was complete.

Ultimately, of course, Hart lost a hard-fought nomination battle to Mondale. After sweeping out New Hampshire to wins in Maine, Massachusetts, Florida and other "Super Tuesday" states, Hart stumbled badly in Illinois, New York and New Jersey. A late charge in Ohio and the June California primary was not enough to block a first-ballot win for Mondale at the Democratic convention in San Francisco.

In 2008, however, the landscape in much different and the prospects for a beneficiary of the Iowa Effect less clear. The intense media scrutiny and dynamics within each party make big surprises - and big bounces - from the Hawkeye State less likely. (Absentee balloting, already underway in 11 states, could further blunt the impact of Iowa.)

On the Republican side, Mitt Romney's entire '08 strategy hinges on the Iowa effect. Hoping to follow in the footsteps of fellow Bay Stater John Kerry four years ago, Romney massively invested in Iowa to upend early favorites Rudy Giuliani and John McCain and then slingshot to victory in neighboring New Hampshire. Team Romney then hoped to ride the wave into South Carolina, Michigan and beyond.

The rise of Mike Huckabee over the past two months puts all of that in jeopardy. But while Huckabee may deny Romney the benefits of the Iowa Effect, the former Arkansas Governor is unlikely to reap them himself. After leaving the evangelical-friendly confines of Iowa, Huckabee faces tough sledding in New Hampshire. And as the scrutiny over his extremist past and present grows, Huckabee's chances will diminish. Huckabee will have peaked too soon. John McCain, back from the dead, may be peaking at just the right time. The biggest open question may be whether Rudy Giuliani's national campaign ever peaks at all.

No doubt, Democrats Barack Obama and John Edwards are each counting on Iowa to provide the needed momentum to overturn Hillary Clinton's commanding national lead. But given the heightened expectations for Obama, it is Edwards who seems best positioned to jump in the polls with a surprise win on Thursday.

Despite his third place showing in the nationwide polls, John Edwards' excellent organization on the ground and strong second place showing in 2004 make him a formidable candidate in Iowa's January 3rd caucus. (Ironically, it was Howard Dean's post-caucus "scream" that hijacked the media attention in 2004, and perhaps robbed Edwards of the New Hampshire bump his surprisingly close 29%-23% race in Iowa might have earned him.)

A solid win in Iowa, especially if coupled with an Obama second place showing over Hillary Clinton, could propel Edwards through the next wave of January voting in New Hampshire, Michigan, Nevada, South Carolina and Florida. While Edwards is second or third in those states, a post-Iowa wave could catapult him to wins and build the media tsunami for the February 5th "national primary."

Ultimately, the chances for a candidate in either party to capture the Iowa Effect may be diminished by both the inundation of media coverage and the "pre-factoring" of expectations. The deluge of polls and the swarms of reporters make surprises less likely. And in much the same way the stock market internalizes in advance future interest rate changes or forecasted movement in inflation or unemployment, expectations for Thursday's Iowa caucus may already be baked into the media narrative to come.

That doesn't mean surprises from Iowa are impossible. In 2008, Iowa's impact may not unexpectedly hurl a new frontrunner to the top of his or her party's race. The Iowa Effect in '08 could just be wide open races in both parties. And that would be compelling theater indeed.