Las Vegas (CNN) -- Most of the remaining Republican presidential candidates spent Friday barnstorming across Nevada -- one day before that state's critical first-in-the-West presidential caucuses.

Front-runner Mitt Romney, Newt Gingrich and Ron Paul crisscrossed the state, focusing in large part on its battered economy. Nevada's has been particularly hard hit by the economic downturn, with a high number of home foreclosures and an unemployment rate that recently soared to an all-time high of 14.9%.

"The president didn't cause this downturn .... but he didn't make it better," Romney told a crowd in Sparks. "He made it worse." Obama used his election "to put through a series of programs that he and his base and his friends thought were important but frankly made it harder for our economy to recover, and so we've suffered," Romney said.

Gingrich, however, hammered Romney, labeling him a "George Soros-approved candidate" -- a reference to the progressive billionaire investor who has become an arch-enemy of conservatives.

"I think we want a candidate who represents Americans who work, pay taxes and believe in the Declaration of Independence," the former House speaker declared.

Former Pennsylvania Sen. Rick Santorum spent the day in Missouri, which holds a non-binding primary on February 7.

"People say the election Tuesday is just a beauty contest ... (but) there are a lot of folks who are looking at these polls across the country and making decisions," Santorum said, arguing that a win on Tuesday could make him more appealing to undecided voters. "This is a must-win state for a Republican if we're going to win the presidency."

Gingrich will not appear on the Missouri ballot. Santorum's team views the state's contest as a way to show a national audience that he's the best conservative alternative to Romney.

On Thursday, Romney, fresh off a primary win in Florida, received Donald Trump's high-profile endorsement at an event in Las Vegas.

Calling Romney "tough" and "smart," Trump said the candidate is "not going to continue to allow bad things to happen to this country."

Trump told reporters he will not mount an independent campaign if the former Massachusetts governor becomes the GOP nominee.

It was unclear whether Trump's decision will have any impact on the Republican race. A Pew survey last month found that 64% of definite and likely GOP voters said an endorsement from the reality television star would make no difference to them.

In the survey, 13% said it would make them more likely to back a candidate, while 20% said it would actually make them less likely.

"Endorsements rarely sway voters," Republican strategist Alex Castellanos said. But "the Trump endorsement undermines (Newt) Gingrich's argument that it is just the Washington establishment that is out to stop him and nominate Romney. Trump is the ultimate outsider."

Meanwhile Thursday, Romney continued to wrestle with fallout from a CNN interview in which he said he wasn't "concerned about the very poor."

"We have a safety net" for the very poor, Romney told CNN's Soledad O'Brien on Wednesday. "If it needs repair, I'll fix it. I'm not concerned about the very rich; they're doing just fine. I'm concerned about the very heart of America, the 90%, 95% of Americans right now who are struggling, and I'll continue to take that message across the nation."

Pressed by O'Brien, Romney noted that the poorest Americans have access to food stamps, Medicaid and housing vouchers.

"You can choose where to focus," he said. "You can focus on the rich; that's not my focus. You can focus on the very poor; that's not my focus. My focus is on middle-income Americans."

Romney later insisted that his words were taken out of context and reiterated the full context of the quote, which was meant to stress his focus on the middle class. "You've got to take the whole sentence, (or else) it sounds very different," he said. "We have a safety net for the poor. ... If there are people that are falling through the cracks, I want to fix that."

Regardless of the extent of Romney's verbal miscue, the former governor is now the clear Republican leader.

A national poll released Wednesday showed Romney in first place with 31% of likely Republican primary voters compared with 26% for Gingrich, 16% for Santorum and 11% for Paul.

The Gallup daily tracking poll had Gingrich ahead of Romney after the former speaker won the January 21 South Carolina primary.

Romney cemented his status as the GOP front-runner with an overwhelming victory in Tuesday's Florida primary. Romney took 46% of the vote, compared with 32% for Gingrich, 13% for Santorum and 7% for Paul, according to the Florida Department of State.

The victory gave Romney all 50 of Florida's convention delegates. Another 28 delegates are at stake in Nevada.