Super Tuesday, March 6, is the largest single day of voting for the four remaining Republican presidential candidates in the race for the party's nomination.
A total of 419 delegates are at stake in 10 states.
Former Massachusetts Gov. Mitt Romney continued to gather momentum after winning the Washington state caucuses on Saturday. It was his fourth straight primary win.
Romney and former Pennsylvania Sen. Rick Santorum are making last-minute appeals to voters in the critical state of Ohio, where polls show a virtual tie just one day before Super Tuesday.
"I'm here to remind you of what makes America great and then I am going to say, 'Well, okay. Let's take these principles and let's apply them to the problems of today," Santorum said.
"Obviously if I got the nod from the people of Ohio, that would send a big statement," he added.
Romney has picked up endorsements from two key conservative leaders, House Majority leader Eric Cantor, R-Va, and Sen. Tom Coburn, R-Okla.
Former House Speaker Newt Gingrich was set to campaign in Georgia, where he began his political career. He has labeled that contest a must-win for his fading presidential bid.
Texas Rep. Ron Paul spent Sunday in Alaska, a state where no other candidates have campaigned in the 2012 primary season.