Baseball's division playoffs started Wednesday to narrow the post-season field, setting the stage for two league champions to meet in the World Series.

Something similar is taking place in the Democratic presidential race. It will determine who becomes Sen. Hillary Rodham Clinton's chief rival for the party's nomination.

Like the early baseball playoff rounds, the political contest also will decide if the ultimate winner has to survive a lengthy, debilitating challenge and whether, despite the front-running former first lady's best efforts, the race pulls the Democrats to the left and damages their general election chances.

Up to five candidates still hope to win the preliminary rounds. But it's mostly a battle between former Sen. John Edwards and Sen. Barack Obama that will be settled in January's Iowa caucuses.

That outcome is in doubt. Iowa has an unpredictable history, and its voters tend to make their choices just before voting. Polls generally show Clinton, Edwards and Obama within a couple of points.

As the showdown nears, Clinton's two main rivals have pursued different strategies — without making much progress.

Edwards has been more aggressive, drawing sharp contrasts whenever possible with Clinton. He has been somewhat more successful than Obama in defining the anti-Hillary case.

In a recent Democratic debate, Edwards sought to contrast their essentially similar Iraq positions by contending that Clinton would keep more U.S. troops in combat than he would.

He has attacked her accepting contributions from lobbyists and political action committees and called her the candidate of "insiders." And he has sought support from free-trade critics, especially in unions, in part by pressing a dubious contention first made by his wife, Elizabeth, that President Bill Clinton and his wife failed to reform healthcare because they turned their focus to the North American Free Trade Agreement.

Edwards also strained credibility in saying he would pass healthcare reform by convincing lawmakers to cut off their own benefits until they passed a bill for the country.

His decision to accept federal funds for the primaries — which will limit his spending in the crucial, early states — was an act of principle, rather than a result of his inability to match the leaders in fundraising, he argues.

His increasingly sharp tone raises questions about how the Edwards strategy will play in Iowa this time. Rejection of negative campaigns by Howard Dean and Dick Gephardt helped John Kerry and Edwards win the top two spots in 2004.

And while he has little choice, his decision to shift resources to Iowa leads one to wonder whether he could follow up if he actually won. Doubts about his long-term prospects could weaken him in Iowa, where, beyond anything, Democrats want a winner.

Obama also faces a dilemma. If he sharpens his tone, he risks undercutting his stance as a unifier who would curb partisanship; if he doesn't, Edwards could outflank him in the battle for anti-war activists.

So far, even while contrasting his early opposition to the Iraq war with Clinton's support, he has maintained a restrained, indirect approach to criticizing her, leaving an impression that he won't go to the mat in order to win.

In marking the fifth anniversary of his original speech opposing the war, Obama never mentioned Clinton on Tuesday, deriding the "conventional thinking" of "some people" who — like the former first lady — contend that in voting to authorize military action, "they weren't really voting for war" but for diplomacy and inspectors.

Obama, too, has stepped up efforts in Iowa, recognizing, like Edwards, that he must win there. "If Barack doesn't win Iowa, it's just a dream," the candidate's wife, Michelle, said last week in Davenport.

Unlike Edwards, Obama has stronger national support and financial resources to benefit from any Iowa success or rebound from a defeat.

The focus on Obama and Edwards has overshadowed other Democrats. Sens. Joseph Biden and Chris Dodd and Gov. Bill Richardson all have some Iowa strength, but their fundraising has lagged. It may take a major implosion from a front-runner for any of them to crack the top three.

As the first contest, Iowa rarely ends a nominating fight. For Republicans, it is likely to be but the first test in a drawn-out battle.

But the entire Democratic race may hinge on whether someone can stop Clinton there — and, if so, who does it.

Carl Leubsdorf is Washington bureau chief of the Dallas Morning News. Reach him at cleubsdorf@dallasnews.com.