MANCHESTER, N.H. (AP) -- Republican rivals for the presidential nomination have a chance to knock front-runner Mitt Romney, who has a commanding lead in New Hampshire polls, off his perch in back-to-back weekend debates that could help define the contest.
In a race largely driven by 13 previous sparring matches, Romney has emerged mostly unscathed by the six or seven opponents who have flanked his debate position on center stage.
That could change with Saturday night's debate or the one scheduled Sunday morning, as rivals Newt Gingrich and Rick Santorum seek to stop Romney's march to the GOP nomination. In particular, Gingrich is looking to keep his candidacy afloat while Santorum hopes to capitalize on his neck-and-neck performance against Romney in Iowa's caucuses.
There are fewer than 12 hours between an ABC News/WMUR debate Saturday and an NBC News/Facebook debate on Sunday's "Meet the Press."
"Two debates! One tomorrow night, one the next morning. Why even stop?" Romney declared Friday at a campaign stop in Tilton. "Why don't we just go right through? It's nonstop!"
Debates can have unforeseen impact. Just days before the New Hampshire primary in 2008, Democratic candidate Barack Obama used that venue to call rival Hillary Rodham Clinton "likable enough" -- a dismissive comment that didn't sit well with her supporters. Obama, who had a significant lead in polls, lost the New Hampshire primary.
Romney's rivals have a serious gap to close in New Hampshire -- and, recent polls show, in upcoming South Carolina. Two surveys out Friday show Romney up at least 20 percentage points over Texas Rep. Ron Paul, his next-closest opponent.
So far, Romney's rivals have been looking past the first-in-the-nation primary state. Santorum has campaigned here but has been peppered with hostile questions about his opposition to gay marriage and comments about homosexuality.
Gingrich has been talking of merely holding Romney's winning total under 50 percent in New Hampshire while Paul, who arrived in the state on Friday, has focused his criticism on Santorum.
"He brags about being for a balanced budget amendment but never did anything about it," Paul said of Santorum's time in the Senate. "He voted four or five times to raise the debt ceiling. He voted to double the size of the Department of Education."
Gingrich, who has made his mark during debates, has aggressively criticized Romney in recent days. He called Romney a "liar" and also said President Obama would laugh at Romney if he were the nominee.
Santorum has also attacked Romney in recent days.
"The only way Republicans lose is if we screw this up and nominate another moderate who has taken multiple positions on every major issue of our time," he wrote supporters in a fundraising appeal.
The former senator from Pennsylvania finished a surprisingly strong second in the Iowa caucuses, coming within eight votes of victory. But he has little time to try to convert that near-victory into a campaign organization in New Hampshire.
As of last month, New Hampshire had about 232,000 registered Republicans, 223,000 Democrats and 313,000 undeclared voters, who can vote in either primary. The state also allows same-day voter registration at the polls.
New Hampshire Secretary of State Bill Gardner says he expects 250,000 ballots to be cast in Tuesday's highly contested Republican presidential primary. In 2008, when both sides had contested races, just over 241,000 ballots were cast in the GOP primary and 289,000 in the Democratic primary.
Looking ahead, a Time/CNN poll in South Carolina showed Romney leading Santorum with 37 percent of the vote.
Santorum is set to leave Sunday for South Carolina for a half-day of campaigning. Romney has events planned in New Hampshire through primary day on Tuesday.