With tracking polls showing several of the candidates gaining in Iowa on front-runner Howard Dean, the inevitable tightening of the race has political pundits wondering if the Democratic primary election could turn into an old-fashioned marathon.

"This thing could go on not only to Feb. 3 — where everybody knows the next big test is in South Carolina and other places — this could go all the way to March 2, where there is a national primary, basically, California, New York, Massachusetts, Ohio, loads of other states on that day, 11 states on that day. That would be a wonderful test of all these guys if it really went to that," said Roll Call Executive Editor Mort Kondracke.

Currently, Dean is remaining on top in New Hampshire and Iowa, according to polls, but a series of knock-abouts, self-inflicted wounds, missteps, gaffes and a pounding from his rivals has voters looking twice, and that hesitation is starting to show up in polls.

In a Wednesday tracking poll by Zogby International, Dean, the former Vermont governor, was favored by 24 percent of Iowa Democrats while Rep. Dick Gephardt (search) of Missouri and Sen. John Kerry (search) of Massachusetts each took 21 percent. Coming in fourth is Sen. John Edwards (search) of North Carolina with 15 percent.

Because the poll has a 4.5 percent margin of error, the results mean that all four men have a shot to win, said pollster John Zogby.

"Kerry now leads among liberals, while moderates belong to Gephardt. The three candidates are bunched together among Democrats. Dean still leads among voters under 50, and Gephardt dominates voters over age 65," he said.

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Iowa is not the only place where Dean is feeling the heat. New polls in New Hampshire, which holds its primary Jan. 27, eight days after the Iowa caucuses, also suggest that the race there may be tightening.

Private polling by two campaigns in the Granite State showed that Dean's lead has shrunk to single digits from a first-of-the-year high of about 25 percentage points, according to officials familiar with the polls.

However, an independent poll, by the American Research Group Inc. (search), showed Dean with 34 percent support and retired Gen. Wesley Clark (search) with 20 percent in the three-day period that ended Monday, far ahead of the rest of the field. Clark is not campaigning in Iowa, and has spent considerable time recently in New Hampshire.

Perhaps noticing the numbers, Dean, who recently took a shot at some of his rivals, but not Clark, in an anti-war ad airing in Iowa, on Wednesday questioned Clark's party loyalty.

"I think Gen. Clark is a good guy. But I truly believe he is a Republican," Dean said to applause. "I don't mean offense to General Clark, he is a good guy and I don't mind that he voted for [former Republican presidents] Nixon and Reagan, that was a long time ago ... What bothers me is that he went out to raise money for the Republican Party and said great things about Dick Cheney, Donald Rumsfeld and George Bush after he knew they were anti-choice, after he tried to put this incredible $3 trillion tax cut through, which hurt women, children and people trying to get their jobs and education."

Clark brushed off the criticism, saying he also voted for Democrats Al Gore and Bill Clinton. He added that it can't hurt when an opponent calls him a good guy.

At least one rival warned that Dean's more aggressive stance could backfire with voters weary of assaults.

"What people are hungering for here in Iowa is a positive, uplifting campaign of hope, which is what my campaign is about," said Edwards.

Edwards, who has risen in the polls enough to be mentioned in the Dean anti-war ad, has been a consistent candidate in Iowa, and could fare better than expected. But one analyst said the candidate is not moving ahead fast enough at this point in the race.

"[Edwards] is everybody's second choice, everybody likes him," said National Public Radio's Mara Liasson. "I think 'surge' is a little too strong a word ... I don't see the kind of surge that would make him be a real true threat to Dean or Gephardt."

Liasson said she believes Dean remains the candidate to beat because even though others are moving up in the polls, she hasn't seen a "depletion in the energy or enthusiasm" of Dean's supporters.

But Weekly Standard editor Fred Barnes said Dean may have plateaued.

"Clearly now, the undecideds are unlikely to go to Dean. I think people have seen Dean in both of these states, they have seen him as the front-runner, as acting almost as an incumbent .... They have seen him, they've checked him out and now they are looking at other candidates," Barnes said.

Fox News' Corbett Riner and Sharon Kehnemui and The Associated Press contributed to this report.