Mitt Romney Turns Attention to Santorum (Update 1)

Updated from 10:41 a.m. ET with Tim Pawlenty's conference call comments

NEW YORK (TheStreet) -- Front-runner Mitt Romney has turned his attacks to Rick Santorum as the former Pennsylvania senator seems to pose the biggest threat in Tuesday's three Republican primary contests.

Minnesota and Colorado voters head to caucus Tuesday while Missouri holds a non-binding primary, and Santorum has polled closest to Romney in those states as the former senator leads the former Massachusetts governor in the latest Minnesota and Missouri polls and holds second in Colorado.

Mitt Romney

"Rick Santorum is part of the big-spending Washington establishment that ran up the national debt by trillions and stuck our grandchildren with the bill," Andrea Saul, a Romney spokeswoman, said in a statement. "His ardent and passionate defense of earmarks is not something that fiscal conservatives are looking for in our next president."

Santorum skipped ground campaigning in Florida ahead of the state's primary and instead bolted west to strengthen his presence in Tuesday's contests, which his campaign targeted as favorable races.

Santorum's retail campaign style makes him a more viable option among voters in caucus states as he is able to motivate supporters to commit to the time-intensive process.

Romney's campaign wasted no time after its landslide Nevada caucus victory to blast Santorum for his past work as a U.S. senator as they had released emails that listed what it considered negative blemishes on Santorum's record.

The emails, labeled as research briefings, slammed Santorum for alleged false attacks on Romney's Massachusetts health care system and for his supposed defense of earmarks and pork-barrel spending.

Romney's campaign held a Monday conference call hosted by former Minnesota Gov. Tim Pawlenty about Santorum's long history of pork-barrel spending, according to a press release.

"Rick Santorum is a nice guy, but he is simply not ready to be president," Pawlenty said in a statement. "Even in the face of crushing federal debt, Rick Santorum voted for the infamous 'Bridge to Nowhere.' That type of leadership will not help us rein in government and slash the unprecedented federal debt."

Pawlenty, who has been a key endorsement for Romney, has campaigned heavily for the former Massachusetts governor, and it appears he will be quite busy through Tuesday as he tries to flip a Minnesota poll that showed Santorum ahead of the GOP front-runner by about two percentage points.