Romney has long been the favorite in Arizona, but his supporters acknowledge Santorum has picked up steam since his Feb. 7 wins in Colorado, Minnesota and Missouri. A recent CNN-Time magazine poll indicated Romney's lead is 4 percentage points and that early voting is expected to boost Romney's chances of notching a win.
But Randy Pullen, a one-time Arizona GOP chairman and a Romney supporter, expressed a nervousness about Tuesday's vote.
Even though he says he thinks Romney is ahead among early voters, Pullen told The Washington Post: "I'm concerned. If there's a big turnout on election day, Santorum might pull it off."
Romney won Arizona and Michigan, which also holds its proportional primary Tuesday, during his 2008 bid to be the party's nominee. Losses in 2012 would point up the inability of the GOP to coalesce around Romney and embrace him as the party's standard-bearer against President Obama in November.
For his part, Santorum, during a recent appearance in Arizona, played up his blue-collar roots in western Pennsylvania when comparing himself to rivals Romney and Newt Gingrich.
"I'm not a manager. I'm not a visionary," he said. "I'm a guy from a steel town who grew up understanding what made this country great."
Mitt Romney may hold the poll advantage in Arizona, but the real story may be the finish of former House Speaker Newt Gingrich, Public Policy Polling President Dean Debnam told CNN.
"The big thing to watch over the next week will be whether Newt Gingrich's supporters stick with him or jump ship to Santorum because he's a more viable candidate," Debnam said. "If that happens this race could get even closer."
Cash-strapped Gingrich has been looking ahead to Super Tuesday, a strategy that may allow Santorum to enter the 10-state voting frenzy March 6 as the consensus alternative to Romney, The Washington Post reported.
"Gingrich can't allow this to continue and still raise money to pay for coffee -- much less a campaign," GOP strategist Dan Hazelwood said.
Looking to November, a recent Public Policy Polling survey indicated Obama should compete -- hard -- in Arizona.
Obama was tied with Romney at 47 percent, a far better position than in November when he trailed by 7 percentage points. PPP results indicate Obama leads Paul and Gingrich by 4 percentage points, 46 percent to 42 percent and 48 percent to 44 percent, respectively. And though he trailed Santorum, it was only by 1 percentage point, 47 percent to 46 percent.
Arizona is considered a divining rod on the fundamental change in voter makeup in the West, Jill Hanauer, president of Denver-based Project New America, told Rolling Stone.
Hanauer said Arizona voters surveyed by her firm indicated they're "sick of ideological fights" and Republican politics that focus on immigration instead of jobs and education.
More than 200,000 people already cast ballots in the Arizona primary as of early last week, several county election officials said.
"I would say turnout is good," Evonne Reed, a public information officer in the Maricopa County Recorder's office, told CNN.