Call it a brave new world in Iowa presidential politics.

The races for both the Republican and Democratic nominations here are toss ups as voting approaches, a double-dose of fluidity unseen in decades. At the same time, the effect of winning — or losing — the leadoff Iowa caucuses in 2008 is anyone's guess.

Will Iowa christen the nominees and give them steam to run the table of rapid-fire primaries? Or will the state set the stage for upsets in next-up New Hampshire five days later?

Regardless of the answer, dogfights on both sides are certain in the five weeks until Iowans caucus.

A poll released Sunday by The Des Moines Register shows both races in dead heats.

With a 4.4 percentage point margin of error, Mike Huckabee had 29 percent to Mitt Romney's 24 percent and Rudy Giuliani's 13 percent. Among Democrats, Barack Obama got 28 percent, while Hillary Rodham Clinton had 25 percent, and John Edwards had 23 percent. Other candidates were in single digits. More than half of likely caucus-goers in both races say they could change their minds. A chunk are undecided.

An Associated Press-Pew poll being released this week echoes the competitive situations in Iowa.

"We haven't had wide-open races on both sides for some time. This is absolutely unprecedented," said David Redlawsk, a University of Iowa political scientist. "And the impact of Iowa is unknown because the environment we're in is different."

For one, the primary calendar is packed tight. The Iowa caucuses are Jan. 3, and New Hampshire votes Jan. 8. Several other states quickly follow, culminating in what amounts to a de facto national primary Feb. 5 when two dozen states hold contests. That could make it difficult for anyone knocked off in Iowa to generate momentum needed for a comeback.

However, the 24-hour news cycle has intensified, with cable channels, talk radio, the Internet, blogs — and mainstream political media Web sites — playing major minute-by-minute roles in the campaign. That could provide Iowa losers with a giant megaphone through which to attack the front-runner or fix their own missteps.

Also, a slew of Republicans and Democrats are running and poised to split the votes in a multitude of ways in Iowa and elsewhere. Candidates may be able to hang in far longer than in past years given that there's so much money being poured into the campaigns; it now can be collected quickly as GOP long-shot Ron Paul proved with a one-day $4.5 million haul.

The other unknowns that could further scramble the contests include the behavior of late-deciders, the impact of outside groups, the candidates' potential unforced or forced errors, and the negative ads expected in the coming weeks.

All that adds up to unpredictability — nationally and in Iowa.

On the Republican side, Romney spent nearly $5 million on TV ads, built a superior state campaign, and held 396 events in Iowa only to watch his months-long lead evaporate as Huckabee — an underdog and a one-time Southern Baptist minister — surged by consolidating the support of influential religious conservatives.

"My conservative message of faith, family, and freedom is resonating with the American people. They know it's authentic," Huckabee said in a statement Sunday, jabbing the former Massachusetts governor, who has battled charges of changing positions for political gain.

But the former Arkansas governor dramatically trails Romney in money and, perhaps more importantly, organization. With limited resources, the future of Huckabee's bid relies on an Iowa win — and the momentum and money that could come with it.

If beat in Iowa, Romney still would be able to compete in New Hampshire, where he leads in polls and has a strong campaign. But a loss would severely set him back.

On Friday, he said he's not surprised the Iowa race tightened. "People have a lot of people to chose from, and as they get to know folks and find things they like about different candidates, that's what you'd expect," Romney said.

He is stepping up his criticism of Huckabee on taxes and immigration. His surrogates also now are arguing to social conservatives that Huckabee doesn't have the money and manpower needed to beat Giuliani, an abortion-rights backer, in contests beyond Iowa.

In the Democratic race, Clinton, the leader in national and most other state polls, is fighting to keep her aura of inevitability in tact and prevent Obama or Edwards from crippling it with an Iowa victory. Despite the former first lady's celebrity, Clinton has struggled to break out of the pack here. Edwards is well known to Iowans from his 2004 race, while other Democrats have warmed to Obama's optimistic message.

Second choices in the caucuses count; Democratic rules allow backers of second-tier candidates to switch to another contender after the first round of caucusing. Undecided voters are a wild card, and Democratic operatives estimate that roughly half of the electorate hasn't chosen who to ultimately support.

As the polls have tightened, Obama has faced more intense criticism.

Clinton assailed the Illinois senator on Sunday for a political action committee he controls that has contributed money to elected officials in early voting states. Asked by reporters if Obama's character was in question, Clinton said in Cedar Rapids, Iowa, "I'm going to let voters make that decision, but it's beginning to look a lot like that."

In Des Moines, Obama brushed off the spike in criticism. "I think that folks from some of the other campaigns are reading the polls and starting to get stressed and issuing a whole range of outlandish accusations," he said.

The stakes are higher for Obama and Edwards than Clinton in Iowa.

If she loses Iowa, the New York senator can rely on her financial and organizational muscle. She's trying to build a firewall in New Hampshire to protect her from an Iowa loss; Obama and Edwards have much less organization there. But the momentum from either of them winning in Iowa could dramatically upend the race. Conversely, a clear win in Iowa for Clinton could cement her front-runner status and make her difficult to beat.