DES MOINES, Iowa — Iowa could make or break a Democratic candidate on Thursday. The question is, who?

While the state has long played a key role in choosing the Democratic presidential nominee, it has unparalleled influence this year, even after several larger states moved up their contests to try and muscle in. Those efforts have done little more than compress the calendar into a five-week sprint that ends with the multistate primary Feb. 5 — strengthening Iowa's position as the leadoff caucus state rather than diminishing it.

Even New Hampshire, which holds the first primary of the season, has seen its once-mighty position diminished somewhat by Iowa's outsized role this time.

Hillary Rodham Clinton, Barack Obama and John Edwards are locked in a tight three-way contest in Iowa just days before voters attend their precinct caucuses on Thursday. And while all three have strong organizations in other early states, the best laid plans in those places could come apart depending on what happens in Iowa.

Only Obama and Clinton have raised enough campaign cash to be sure of being competitive through Feb. 5 and beyond. Edwards has agreed to accept federal matching funds, which will constrain the amount of money he is allowed to spend in each state.

Trailing in the polls, Bill Richardson, Joe Biden and Chris Dodd have also concentrated nearly all their resources in Iowa in hopes of scoring an upset.

The impact of unexpected news events, such as the assassination of former Prime Minister Benazir Bhutto in Pakistan, may further complicate a fluid situation.

Here's a look at what to expect in the next several weeks:

Iowa: Jan. 3

All six major Democratic candidates will blitz Iowa, which has 45 pledged delegates, before Thursday's caucuses. Hundreds of staff and volunteers from each campaign will flood likely caucus goers with mail, visits and phone calls. The television airwaves have been saturated for weeks with advertising.

Clinton, who has struggled in Iowa despite leading the field in national and most other state polls, has the most riding on the outcome here. A win could fuel a wave of momentum for the former first lady, while a loss, particularly to Obama, would shatter the notion of inevitability she has tried to project.

The New York senator is barnstorming the state and has deployed dozens of surrogates including her husband, former President Bill Clinton. Her closing argument — "It's time to pick a president" — underscores her central message: A candidate like Obama may inspire and move voters, but Clinton is the best prepared to actually do the job.