The Republican presidential field heads west to Nevada this week facing a single dominant question: Can anything or anyone block Mitt Romney’s path to the GOP presidential nomination, particularly given his resounding win here four years ago?

Romney has the best organization of any of the remaining candidates, and he has spent plenty of time here since 2008. He will arrive with momentum from his decisive win in Florida on Tuesday, and Nevada’s sizable Mormon population gives him an edge, too.

In 2008, Romney won 51 percent of the vote, and Rep. Ron Paul (Tex.) finished second with 13 percent.

But Nevada is not without advantages for the other candidates. Saturday’s “first in the West” caucuses are expected to favor campaigns with loyal supporters willing to trudge out to a caucus meeting on a weekend morning. This year, that helps Paul, who has been developing solid organizations in all the caucus states to turn out supporters, and his organization is significantly stronger today than it was four years ago.

Newt Gingrich is betting on a wild card here, the tea party movement. Tea party sentiment is strong in the state and helped nominate Sharron Angle two years ago in a primary to challenge Senate Majority Leader Harry M. Reid (D). Gingrich is playing an underdog’s game of catch-up in Nevada. He has little money in the bank and only began investing here a few weeks ago. But he boasts another noteworthy asset: billionaire casino owner Sheldon Adelson, a top supporter who has given a pro-Gingrich group $10 million and is being closely watched to see whether more is on the way.

The backdrop for all of this is that Nevada is a critical swing state that has marched through much of the Obama years with the nation’s highest unemployment and foreclosure rates. The area around Las Vegas, home to three-quarters of Nevadans, is a bastion of independent voters who resoundingly chose President Obama four years ago. The eventual Republican nominee must not only beat his GOP rivals Saturday but also reach out to these critical voters, many of them disaffected by the current administration.

“Two-thirds of this country believe America is worse off than when President Obama took office,” said Whit Ayres, a Republican pollster who most recently worked for a PAC supporting Jon Huntsman Jr. “In some ways the voters in Nevada are a microcosm of President Obama’s problem. They bought into this hope-and-change malarkey, and now all they see is that the economy has gotten worse.”

Despite that, Nevada caucus-goers are anything but a microcosm of the general electorate. In 2008, 44,000 Republicans, or less than 1 percent of the electorate, attended Nevada caucus meetings. And Republicans are not optimistic that turnout will be much higher this year. The Nevada GOP has done little to spread the word about the caucuses, and Nevadans, unlike voters in Iowa, New Hampshire and South Carolina, are less familiar with their new electoral ritual, which was moved to the top of the presidential calendar only four years ago.

This year’s caucuses are unusual. Republicans will gather in 125 caucus locations across the state. But county GOP committees were allowed this year to set their own rules, so start and finish times will vary — and results will trickle in over the day.

In addition, a special nighttime caucus was added in Las Vegas to accommodate observant Jews unable to caucus during the Sabbath. The caucus, to be held at the Miriam and Sheldon G. Adelson Educational Campus, drew protests from Republicans who assumed that Adelson, the Gingrich backer, was engineering an advantage for his candidate.

An Adelson spokesman, Ron Reese, issued a statement Monday saying the Adelsons had “no involvement” in the decision. Reese said an Orthodox Jew who sits on the Adelson school’s board brought the matter to the attention of the Clark County GOP.

The Adelsons “were informed by the headmaster of the school after the final decision had been agreed upon,” Reese said.

In the meantime, voters can expect the same battle lines that have characterized the Republican contest in recent days to hit Nevada now — but with much less spending on TV ads because the target audience is so small.

Gingrich will continue to portray Romney as too similar to Obama to provide the contrast needed to defeat him in the fall — and continue to accuse him of lies in his campaign rhetoric against Gingrich. Gingrich spokesman R.C. Hammond said their goal is to turn out the tea party; the former House speaker has attracted praise from Angle, even though she has stopped short of endorsing him.

“The farther west you get, the more ‘conservative’ matters,” Hammond said. “They look at somebody like Romney who on his best days is misleading and on his worst days is flat-out lying. Then you look at Gingrich, a straight shooter. You have that contrast. That’s why it’s important to get the tea party crowd out to get the momentum building there.”

In addition, a pro-Gingrich super PAC (the one bankrolled by Adelson) will play a big role in Nevada; the group began building its own organization in the Silver State a few weeks ago. Chuck Muth, a prominent conservative organizer in Nevada (and erstwhile Paul supporter), is leading the PAC’s efforts here.

Romney spokesman Eric Fehrnstrom, meanwhile, said the former Massachusetts governor will continue to hit Gingrich on his consulting work for Freddie Mac.

“It’s hard to justify cashing in on Freddie Mac when the people of Florida were losing their homes,” Fehrnstrom said. “And I think that problem exists for him in Nevada as well.”

The candidate investing the least in Nevada is former senator Rick Santorum of Pennsylvania. , who has lost virtually all the momentum from his Iowa caucus win in early January. Santorum, who left Florida over the weekend to tend to his ill daughter, scheduled his Florida primary party in Las Vegas on Tuesday night — but will spend much of the week in Colorado, which holds its caucuses Feb. 7.

Staff writers Nia-Malika Henderson in Boca Raton, Fla., and Philip Rucker in Tampa and staff researcher Lucy Shackelford in Washington contributed to this report.