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, meanwhile, 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.
Paul sat down for an interview with CNN's Piers Morgan, then later addressed a crowd of Filipino-American veterans in Las Vegas. Even with a national poll suggesting he is last among the four remaining candidates, he expressed confidence in his candidacy and that his stability and consistent principles could succeed.
"I think the record of this campaign, the Republican campaign, shows you that a lot of the candidates are coming and going," Paul told CNN. "But one thing that's characteristic of our campaign is steady growth."
Former Pennsylvania Sen. Rick Santorum spent the day in Missouri, which holds a non-binding primary on February 7. County caucuses in that state will be held March 17, to select delegates for congressional district conventions and the state convention.
"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.
Santorum's campaign suffered a blow Friday, when the Indiana Republican Party announced that he wouldn't be on that state's May 8 primary ballot. The state party said Romney will officially be on the ballot, while Gingrich and Paul submitted enough signatures but they still must be certified by the Indiana's secretary of state by February 10.
After an event at William Woods University in Missouri, Santorum told reporters that he fell 24 signatures short because the party changed their rules in the middle of the game. He said his campaign "absolutely" will challenge the decision.
Of the four current candidates, Romney appears to have the momentum fresh off his primary win in Florida. And on Thursday, business tycoon and reality television star Donald Trump endorsed him 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."
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.
CNN's Adam Aigner-Treworgy contributed to this report.