(CNN) -- Front-running presidential candidates in both parties sniped at each other Saturday night as they debated three days before Tuesday's first primary.
Sen. John McCain, left, and Fred Thompson, center, shake hands with debate moderator Charles Giblson.
Republicans John McCain and Mike Huckabee seemed to be working off the same playbook, each hitting rival Mitt Romney for changing his position on key issues.
And Democrat Hillary Clinton pointedly criticized rival Barack Obama, seeking to paint him as a flip-flopper on key issues.
No longer the party's clear front-runner after her third-place showing in Iowa, Clinton went after the Illinois Democrat at the top of the debate for what she called shifted stances on the Patriot Act and Iraq war funding.
"Well, you've changed positions within three years on, you know, a range of issues that you put forth when you ran for the Senate, and now you have changed," Clinton said. "You said you would vote against the Patriot Act. You came to the Senate; you voted for it. You said that you would vote against funding for the Iraq war. You came to the Senate, and you voted for $300 billion of it." Watch Clinton discuss her "likability" »
Obama immediately took issue with Clinton's characterization, and hit back saying, "I think the people of America are looking for are folks who are going to be straight about the issues and are going to be interested in solving problems and bringing people together."
The crucial debate in Manchester, New Hampshire, came the same day a CNN/WMUR poll out of the Granite State showed the two candidates locked in a dead-heat, each drawing 33 percent of support among likely Democratic voters in the state.
On the Republican side, the poll showed McCain had taken a lead over Romney among New Hampshire Republicans, 33-27 percent. Romney, former governor of neighboring Massachusetts, had led polls in the Granite state through most of 2007 but the Arizona senator had closed the gap through December.
Huckabee, fresh from his big win in the Iowa caucuses, defended his statements criticizing President Bush's foreign policy for reflecting an "arrogant bunker mentality."
"I was speaking to the fact that there were times when we gave the world the impression that we were going to ignore what they thought or what they felt, and we were going to do whatever it is we wanted to do," Huckabee said.
Romney -- the candidate Huckabee defeated in Iowa and sat next to during the debate -- pounced on Huckabee's remarks.
"The president is not arrogant. The president is not subject to a bunker mentality," Romney said. "The president has acted out of his desire to keep America safe. And we owe him a debt of gratitude for keeping this country safe over the last six years." Watch candidates spar over Bush's foreign policy »
During the spirited discussion on foreign policy, Romney told Huckabee, "Don't try and characterize my positions."
"Which one?" Huckabee then immediately asked, prompting the hundreds of journalists watching the debate from the Saint Anselm College filing center to burst into laughter.
"We disagree on a lot of issues, but I agree you are the candidate of change," McCain told Romney later in the debate, after the former Massachusetts governor said he was best able to change Washington.
Romney also sparred with McCain on the issue of immigration, calling his plan to provide a legal path to citizenship for some undocumented immigrants a form of amnesty. Romney has been airing television ads critical of McCain's position in New Hampshire. Watch Romney and McCain square off on immigration »
"It's not amnesty, and for you to describe it as such in your attack ads, my friend -- you can spend your whole fortune on these attack ads, but it still won't be true," McCain shot back.
"Is there a way to have this about issues and not personal attacks? I hope so," Romney responded.
Former New York Mayor Rudy Giuliani said his priority as president would be dealing with undocumented immigrants who have committed crimes.
"Since you can't throw out all 12 million people, whether Governor Romney would like to do that or not or anybody else would, you just can't do it. It's not physically possible to do."
Meanwhile, Ron Paul decried the country's economic policies.
"[Inflation] comes from deficit financing with this war-mongering foreign policy we have. We run up the deficits. We tax. We borrow. We borrow from the Chinese. We can't borrow enough," the Texas congressman said.
Later, each candidate was asked to compare himself with the campaign of Democratic presidential hopeful Obama and why he should receive the support of independents.
All the Republicans distanced themselves from Obama's views -- which Fred Thompson called "liberal" -- except for Huckabee, who talked about the enthusiasm of Obama's supporters and the public's desire for a president to transcend divisions of political parties.
Questions about foreign policy also kicked off the Democratic debate.
Obama said he stood by his statements that he would go into western Pakistan if he had actionable intelligence pointing to terrorists regrouping in the region.
"We have a situation where al Qaeda -- a sworn enemy of the United States, that killed 3,000 Americans and is currently plotting to do the same -- is in the territory of Pakistan. We know that," Obama said.
"My job as commander in chief will be to make sure that we strike anybody who would do America harm when we have actionable intelligence do to that."
The candidates also expressed concern about the political situation in Pakistan and its leaders.
Former North Carolina Sen. John Edwards called Pakistani President Pervez Musharraf an "unstable leader." New Mexico Gov. Bill Richardson said he would ask Musharraf to step down. But Clinton disagreed.
"If you remove Musharraf and have elections, that's going to be very difficult for the United States to be able to control what comes next," she said.
Clinton went on the attack when the subject turned to health care, saying Obama has changed his views on the issue enough times to lead The Associated Press to write that "he could have a pretty good debate with himself." Watch Democrats debate health care issues »
"Well, you know, I think The Associated Press was quoting some of your folks, Hillary," Obama shot back.
Edwards then urged the candidates -- particularly Clinton -- to stop attacking each other.
"I didn't hear these kind of attacks from Senator Clinton when she was ahead. Now that she's not, we hear them," Edwards said.
On the Iraq war, Edwards said he would pull 40,000 to 50,000 troops out of the war zone "very quickly" during his first year as president.
Richardson said he would withdraw all the troops in one year.
"My whole point is that this whole campaign, everything we talk about -- universal health care, improving schools, helping kids -- cannot happen until we get out of this war, because the Congress and the president basically have a dysfunctional relationship where nothing gets done," Richardson said.
But there were also lighter moments during the debate.
Clinton was asked how she felt about voters hesitating on the "likability issue."
"That hurts my feelings, but I'll try to go on," she said to laughter. "I don't think I'm that bad."
Saturday night's debate -- sponsored by ABC News, Facebook and WMUR -- was the last opportunity for the candidates to duke it out on the same stage before New Hampshire voters have their say.
In order to participate in Saturday evening's debate, candidates had to either finish in the top four in Iowa or get at least 5 percent in recent New Hampshire or national polls.
Joe Biden and Chris Dodd dropped out of the Democratic race after disappointing finishes in Iowa.
The campaign for Democratic hopeful Dennis Kucinich, who didn't make the threshold for the debate, filed a complaint with the Federal Communications Commission, saying that ABC is "violating its obligation to operate in the public interest" by not letting him participate.
The debates come after Iowa wins for Huckabee and Obama, but in the Granite State, different leaders could emerge.
Clinton and Obama are tied at the top among Democrats, and McCain is leading the GOP pack, according to results from a new CNN WMUR/New Hampshire presidential primary poll.
The survey was conducted by the University of New Hampshire. Clinton and Obama each grabbed the support of 33 percent of New Hampshire voters who said they plan to vote in the state's Democratic primary.
Twenty percent said they would vote for Edwards. Four percent chose Richardson, and 2 percent chose Kucinich.
On the Republican side, 33 percent of likely Republican primary-goes in New Hampshire said McCain was their top pick. Coming in second was Romney with 27 percent.
Giuliani had 14 percent, followed by Huckabee with 11 percent, Paul with 9 percent and Duncan Hunter and Thompson with 1 percent each.
The poll, released just hours before the debate, has a margin of error of plus or minus 5 percentage points. E-mail to a friend
CNN Ticker producer Alexander Mooney contributed to this report.