"This is crunch time," said former Democratic Sen. , and he spoke for all.
In a race without front-runners, a brief Christmas lull yielded quickly in both early-voting states to a new round of subtle digs, outright criticism, fresh TV ads and stepped-up efforts by independent organizations.
Forty percent of Iowa's voters are still undecided, reports CBS News chief White House correspondent Jim Axelrod. Iowans traditionally make up their minds very late - and it looks this year will be no exception.
"It's closing time in Iowa and anyone who says they know who will emerge as winners eight days from now needs to be checked for post-eggnog distress syndrome," CBSNews.com senior political editor Vaughn Ververs said. "The easy part is identifying the candidates and reciting the messages they've woven over a year of speeches, debates and ads. Now comes the hard part - closing the sale among those voters who will show up at the caucuses on January 3rd." (Read more from Ververs in Horserace)
Former Arkansas Gov. , surprise leader in the Republican pre-caucus polls, with a .12-gauge shotgun and said caucus-goers on Jan. 3 should take notice.
"Maybe it will show that I certainly understand the culture of being outdoors," he said. It was a not-so-subtle jab at his leading rival in the state, . The former Massachusetts governor once proclaimed himself a lifelong hunter, but later conceded he had shot only "small varmints" and did not have a gun or a hunting license.
Romney's political quarry for the day was Arizona Sen. , seemingly staging a comeback in New Hampshire. Romney accused his rival of flip-flops on immigration and tax cuts.
"The point is that under his bill, that he fought for, everybody who came here illegally could stay forever. And does he still believe that or does he not believe that?" Romney said on a radio program from New Hampshire.
"And likewise on taxation. He said, well now he's for making the Bush tax cuts permanent. Well, does he admit he was wrong in voting against them before?
McCain responded quickly.
"I know something about tailspins, and it's pretty clear Mitt Romney is in one," said the former front-runner. "It's disappointing that he would launch desperate, flailing and false attacks in an attempt to maintain relevance."
In the short term, the Republican race has become a pair of separate but connected two-man campaigns in early states. In Iowa, Huckabee, a former Baptist minister, is counting on the support of evangelical Christians to deliver a victory over Romney, who has spent millions in the state.
McCain is not mounting a significant effort in Iowa, but his hopes in New Hampshire - where he won the primary eight years ago - depend heavily on the outcome. A Huckabee victory, McCain's aides say, would put their man in much better position to defeat Romney in the first primary five days later.
By contrast, the Democratic race over the next eight days shapes up as a three-way fight for Iowa among Sens. and and Edwards, the party's 2004 vice presidential nominee. It's unlikely that Edwards, in particular, could sustain a loss in the first contest, particularly since he's been campaigning there virtually since the last election.
The latest information on the primary and caucus dates in 2008.
Obama was first among the leading contenders into the state after the holiday, renewing a campaign-long attempt to cast himself as an agent of change while trying to pre-empt Edwards' attacks on special interests in Washington.
At every turn, Obama reminded his Iowans that , reports CBS News correspondent Dean Reynolds.
"Don't let this opportunity slip away," he said.
Obama's drawing power was undimmed by the two-day Christmas layoff. He turned empty halls into packed auditoriums and laid out his case for changing Washington, while mocking his political rivals who says have picked up the same pitch.
Without naming Clinton, he said, "We're told that the lobbyists and the special interests, it's inevitable that they run things, and so the best you can do is to find somebody who knows how to work the system in Washington. ...
"That's essentially the argument that's being made in these last seven days. Don't try something different because that's going to be too risky. You don't know what you might get."
Later in the day, Obama blamed negative advertising and mail sent by unnamed opponents for planting "seeds of doubt" about him.
"That's how Washington typically reacts to change," he said.
The former first lady campaigned with her husband by her side, opening a final-week sprint with remarks designed to blunt Obama and Edwards.
"Some believe you can get change by demanding it, and some believe you can get change by hoping for it," she said in Mount Pleasant, Iowa. "I believe you can get change by working really, really hard for it."
"And I think it takes strength and experience to be able to make change in our political system," she said. "We don't have any time to waste."
Edwards was in Conway, N.H., where he had a succinct appeal.
"You'd better choose someone as your candidate who's ready for this battle. Nice words will not change anything," he said.
Several campaigns unveiled new television commercials during the day, including Edwards, Clinton and McCain, who was going on the air for the first time in South Carolina. (Watch campaign ads on CBSNews.com)
The Alliance for a New America, a pro-Edwards group with ties to his 2004 campaign manager, began airing a commercial in Iowa, and the Club for Growth, a conservative group, announced it would devote additional funds to criticizing Huckabee in Iowa.
Independent records showed Obama had committed to the most Iowa advertising spending of any Democrat, about $7.5 million so far. A spokesman said the Illinois Democrat was being outspent, though, when the efforts of independent groups were figured in. Clinton, a New York senator, has the support of union groups.
Among Republicans, Romney's $5.2 million spent on ads dwarfs all others, raising his prospects but also the stakes if he should lose to an underfunded Huckabee.