Crisscrossing Iowa in pursuit of a strong finish in Tuesday's caucuses, the Republican presidential candidates are trying to keep their eye on the prize -- using their final pre-primary moments to hammer President Obama in between potshots at each other. 

The candidates, after being drawn into battle with the rest of the GOP field, tried to remind audiences Saturday of their displeasure with the incumbent president and convince them that they are the best choice to take him on. 

Rick Santorum, the socially conservative former Pennsylvania senator whose Iowa poll numbers have climbed in recent days, released a TV ad in Iowa Saturday stressing his electability. 

"Who has the best chance to beat Obama? Rick Santorum," the ad declared, describing the him as a "full spectrum conservative" with "more foreign policy credentials than any candidate." 

Santorum plans to air the same ad next week in New Hampshire ahead of that's state lead-off primary. But three days before the Iowa contest, Santorum stayed focus on his ground game there, holding a meeting with more than a dozen local pastors at a coffee shop. 

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Mitt Romney, who is leading the Iowa field alongside Ron Paul in recent polls, is trying to strike a similar balance. He made a quick stop Saturday morning in New Hampshire, a must-win state for Romney, before returning to Iowa. 

In the Granite State, the former Massachusetts governor focused sharply on Obama. 

"This president has been a failure," he said. "I don't think he's a bad guy. I just think he's overwhelmed and is over his head." 

Romney assailed Obama's record on federal spending and job creation, describing his legacy as a "footnote in history." 

In Iowa, Newt Gingrich went after the Obama administration over the Justice Department's move to challenge a South Carolina voter ID law. 

Gingrich, in Council Bluffs, said the administration wants to "steal elections," describing Attorney General Eric Holder as the "junior version" of Obama. 

Gingrich also told Iowans that if they choose him on Tuesday, he will challenge Obama to seven debates -- joking that he would allow the president to use his "Obamaprompter." 

In Fort Dodge, Iowa, Rick Perry slammed the president's health care overhaul as the country's "most onerous" regulation on the horizon. However, the Texas governor couldn't resist taking a shot at Santorum, criticizing him for voting in favor of debt ceiling increases while he was in office and for backing earmarks in his state. 

Perry and Santorum are both competing for evangelicals and other social conservatives in Iowa, which could explain why Perry has been the toughest on Santorum since his poll numbers started to rise. 

Perry again stressed Saturday that he's the outsider in the race. "They're part of the problem," he said on Fox News of his opponents. "They're not the solution." 

The Iowa polls have fluctuated wildly leading up to Tuesday's contest. 

Perry seems to have crept back into the middle tier, while Santorum's momentum has brought him very close to the frontrunners in recent surveys. 

Paul and Romney have traded the lead, though Paul was not in Iowa Saturday. Gingrich has steadily plummeted in the polls, under a multi-million-dollar barrage of negative ads in the state. 

While vowing to stay positive, the campaign has started to look beyond Iowa to South Carolina, where the former speaker could be poised for a strong showing. 

Rep. Michele Bachmann, who won the summertime Ames Straw Poll in Iowa, is meanwhile polling in the single digits in many recent surveys. Former Utah Gov. Jon Huntsman is not campaigning in Iowa at all, instead aiming for a respectable turnout in New Hampshire the following week.