Romney spent the first part of the day in New Hampshire while most of his GOP rivals rumbled through Iowa's small towns by bus in a final, frenzied dash of retail politicking before the Iowa caucuses in exactly one week.
"I'm not exactly sure how all this is going to work, but I think I'm going to get the nomination if we do our job right," Romney said inside a packed dining room at the Coach Stop restaurant in Londonderry, N.H.
Ignoring his GOP rivals, the former governor targeted President Barack Obama instead, accusing him of trying to turn the U.S. into an "entitlement nation."
Romney also signaled another line of attack against the Democrat in which he would ask voters, "Do you think you're better off than you were four years ago?"
"We know the answer to that one," Romney said with a smile.
Meanwhile, a 2006 memo by Gingrich showed that he once praised the health care law Romney put in place in Massachusetts as governor. Romney's rivals, including Gingrich, have tried to tar him for enacting the series of health care changes.
Gingrich called the law "the most exciting development of the past few weeks" and one with "tremendous potential to effect major change in the American health system."
The memo from Gingrich's Atlanta-based Center for Health Transformation came to light Tuesday, first reported by The Wall Street Journal, as Gingrich followed the lead of two of his rivals and hopped on a bus for a 22-stop tour of Iowa.
Texas Gov. Rick Perry and Minnesota Rep. Michele Bachmann resumed bus tours they had halted because of Christmas.
Romney was headed to Iowa later Tuesday to deliver a speech and then begin a campaign bus trip of his own.
Gingrich's memo noted shortcomings in the law but he went on to note that "we agree entirely with Gov. Romney and Massachusetts legislators that our goal should be 100 percent insurance coverage for all Americans."
Gingrich and others have argued that the Massachusetts law undercuts Romney's conservative credentials. Gingrich also has faced questions about his past support for an individual health care mandate, which conservatives hate.
Gingrich spokesman R.C. Hammond said the memo was "old news that has been covered already."
"Newt previously supported a mandate for health insurance and changed his mind after seeing its effects," Hammond said. "The real question is why 'Mitt the Massachusetts Moderate' won't admit that health insurance mandates don't work."
In the final week of campaigning in Iowa, Bachmann, Perry and Gingrich all were trolling for support handshake by handshake and hoping to create something of a roadblock for Romney, who is looking stronger than expected in the state.
There will be speeches, meet-and-greets, stops at diners and pizza parlors, town hall-style events and a final advertising push that some observers expect will be nasty.
The campaigns are also trying to gauge the level of enthusiasm for Rep. Ron Paul of Texas, who was returning to Iowa on Wednesday.
Recent polls suggest the libertarian favorite, who has a strong operation here, has pulled even or even ahead of Romney - and drawing scrutiny.
"There's really three primaries going on here," former Sen. Rick Santorum of Pennsylvania told reporters Monday in Adel, where he went hunting for pheasant and quail. "There's the libertarian primary, which Ron Paul is going to win. Then you've got the moderate primary, which Gingrich and Romney are scrumming for. And you've got three folks who are running as strong conservatives."
He included himself, Bachmann and Perry in that conservative camp.
Former Utah Gov. Jon Huntsman signaled early on that he would not compete in Iowa, choosing instead to try to make his stand in New Hampshire.
Bachmann is on a mission to visit each of Iowa's 99 counties, an ambitious pace that left her darting into diners and gas stations for quick visits. She was resuming her tour Tuesday and was set to have visited another 10 counties by nightfall.
Perry planned four stops Tuesday. Gingrich scheduled three.
Many of those expected to participate in the caucuses remain undecided, according to the polls, and most of the contenders have seen their fortunes rise quickly and then fall. Romney and Santorum have remained relatively steady, with Romney solidly near the top and Santorum consistently struggling to build support.
Yet Santorum alone has achieved the feat of visiting all 99 counties. With more than 350 campaign events behind him this year, he is hoping the early groundwork - and a possible late surge - help him beat expectations.
He was beginning Tuesday in Iowa's deeply conservative far northwest corner.
Associated Press writers Steve Peoples in New Hampshire and Shannon McCaffrey in Iowa contributed to this report.