GOLDEN: Mitt Romney hopes for another big caucus win in Colorado Tuesday, as his well-oiled campaign machine works to cement his position as the Republican US presidential front runner.
Polls suggest he should triumph easily in the western US state -- where he scored 60 percent in 2008 -- although there is a tighter race in Minnesota, where last-placed Rick Santorum is hoping to snatch a win.
His main rival Newt Gingrich is meanwhile battling to stay in the race after two heavy losses in a row to the former Massachusetts governor, who won in Florida last week and then Nevada at the weekend.
Romney is on a roll in his bid to become the Republican Party's nominee to take on President Barack Obama in the general election in November, having taken three of the five state polls so far.
His financial and campaigning muscle were on display on the eve of Tuesday's caucuses, when he held a rally in a school sports hall almost literally filled to the rafters.
"Mitt, Mitt, Mitt" chanted several thousand supporters packed into the Arapahoe High School hall, with others forced to listen through loudspeakers in a neighboring hall as Romney gave a cheer-buoyed version of his stump address.
By contrast Gingrich spoke to a few hundred supporters in a barely half-full hotel ballroom in Golden, west of Denver, drawing cheers notably with an attack on Romney's gaffe last week about the very poor.
"He said last week that he didn't really worry very much about the very poor because after all they had a safety net," he said, calling Romney's verbal stumble "backwards" in terms of traditional conservative thinking.
The candidates are battling for the biggest share of the 1,144 delegates at the Republican Party's convention in Tampa, Florida, in August. After Nevada Romney how has 99, against 33 for Gingrich, 15 for Paul and 11 for Santorum.
Full results for Nevada published Monday gave him 50 percent, more than twice his nearest rival former House Speaker Gingrich on 21 percent, with Paul snapping at his heels on 19 and Santorum on 10.
In Colorado it might not be that crushing, but should still be comfortable: a Public Policy Polling (PPP) survey Sunday put Romney on 40 percent, Santorum on 26 percent, Gingrich on 18 and Paul on 12 percent.
While the Colorado result is barely in doubt, Romney could see his momentum slowed by a narrow victory -- or even a loss -- in the heartland state of Minnesota.
He was in a statistical tie with conservative darling Santorum, who is hoping to carry Minnesota's caucuses on Tuesday with the help of the state's large base of evangelical Christian and ultraconservative Tea Party voters.
Santorum, who has seen his campaign flag after scoring an early victory in Iowa's first-in-the-nation caucus, is hoping for another upset in Minnesota's non-binding caucus, where turnout is expected to be low.
Romney -- who carried Minnesota in 2008 with 41 percent of the vote -- has not returned to the midwestern state since last week, relying instead on former Minnesota Governor Tim Pawlenty to press his cause.
"The is the only candidate in the race who hasn't spent the bulk of his adult life either in Washington DC or in a parasitic relationship with Washington is Mitt Romney," Pawlenty told a group of around 40 supporters gathered at Romney's suburban Minnesota headquarters.
While the Republicans slug it out on the ground, Obama saw his approval rating soar Monday to the 50-percent mark, with a double-digit lead over Romney, seen as his likely Republican opponent in November.
Obama leads Romney 51 to 45 percent among registered voters, according to a poll by the Washington Post and ABC television.