Atlantic, Iowa (CNN) - After days of cautious stump speeches on patriotism and economic renewal, Mitt Romney went sharply on the offensive Sunday, making oblique jabs at his rivals and attacking President Barack Obama for his Iran policy.
Speaking to members of the media at a crowded diner in Atlantic, Romney laid out contrasts with several of his GOP rivals as the Tuesday caucus date grew near.
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Asked to compare himself to former Sen. Rick Santorum, whose surge in the Iowa Republican race comes within days of voting, Romney pointed to Santorum's 2008 endorsement.
"Sen. Santorum was kind enough to endorse me last time around," Romney said. "I appreciate that."
In an NBC interview Sunday, Santorum said he backed Romney last cycle to try to prevent Sen. John McCain from securing the GOP nomination.
Romney went on to compare Santorum to former House Speaker Newt Gingrich, who Romney has characterized as a Washington insider.
"Like Speaker Gingrich, Sen. Santorum has spent his career in government, in Washington," Romney said. "Nothing wrong with that, but it is a very different background than I have."
Romney was also asked to respond to Gingrich's comments earlier Sunday that Romney would buy the election "if he could."
Gingrich was referencing a slew of television advertisements that have attacked the former speaker, including many produced by a super PAC supportive of Romney's candidacy.
The super PAC is prohibited from coordinating with the Romney campaign, but the former Massachusetts governor has refused to repudiate the attack ads.
On Sunday, Romney responded to Gingrich's charge that he was attempting to buy the election by pointing to the former speaker's fundraising totals.
"Speaker Gingrich I think announced that he raised 10 million this quarter," Romney said. "He ought to be proud of that. We're working hard to raise funds as well."
Romney said his campaign would announce it raised more in the fourth quarter of 2011 than in any previous quarter. He raised over $18 million in the second quarter of his campaign.
The GOP candidate also made the rounds at the Family Table restaurant, which was uncomfortably jammed with supporters, restaurant patrons and members of the media.
Romney kept his criticism trained on Barack Obama when he spoke to the Atlantic audience, and called Obama's term a "failed presidency."
"I want to make sure that the people in this nation understand that he failed us not only at home, he's failed us in dealing with the gravest threat we face, which comes from Iran overseas," he said.
He faulted Obama for pursuing an "engagement policy" with Iran, which this weekend announced a breakthrough in its nuclear capabilities.
"We now know how well that engagement policy has worked," he said of Obama. "What's happened is that those crippling sanctions never got put in place. When voices of dissent went to the street he was silent."
The retail stop comes in the middle of a 771 mile bus tour through Iowa. Romney has made fewer than 10 trips to Iowa this campaign cycle, but is at the top of the field going into the Tuesday caucuses.
Romney told reporters he had worked to build organization in many states to ensure he could become the nominee.
"This is a process that begins here, gets a big boost here, but goes on across the nation and it's been important to me to make sure that I have a team and a capability to go the full distance," he said of Iowa.
Regarding Tuesday night's voting, Romney said he was encouraged by the enthusiasm and size of the crowds turning out to support him.
"I'm pretty confident we'll have a good night," he said. "I don't know who's going to win, but I think we're going to have good support."
– CNN Political Correspondent Joe Johns and CNN Political Producer Shawna Shepherd contributed to this report.