By Sam Youngman and Ros Krasny LAS VEGAS (Reuters) - After stumbling with remarks suggesting he was indifferent to America's poor, Republican White House hopeful Mitt Romney was endorsed on Thursday by one of the country's most famous wealthy businessmen - real estate mogul and reality television star Donald Trump. Trump, who put his own net worth at up to $7 billion, said he was backing Romney in the race for the nomination to oppose President Barack Obama in the November 6 election because of his knowledge of the economy. "Mitt is tough, he's smart, he's sharp," Trump said, standing before a line of American flags at his Trump International Hotel, Romney and his wife, Ann, to his right. You can do it," Trump said. He said he was willing to campaign for Romney and would consider donating to his Super PAC - the independent political group spending tens of millions of dollars in support of Romney. Romney cemented his position as Republican front-runner by trouncing rival Newt Gingrich in Florida's primary on Tuesday, and holds a strong lead in polls of likely Nevada voters ahead of the state's caucuses on Saturday. The ex-Massachusetts governor and former private equity executive says his private sector experience makes him the best candidate to right the troubled U.S. economy. He praised Trump's business acumen as he thanked him for his support. Trump's support could backfire on Romney, the son of a former governor and corporate chief executive who is worth some $270 million. Romney's comments about poor Americans on Wednesday, during what should have been a victory lap after his Florida triumph, underscored the challenge he faces convincing voters hit by the economic downturn he can relate to their problems. "I'm not concerned about the very poor, we have a safety net there," Romney said on CNN. If it needs repair, I'll fix it. Trump cultivates an aura of glitz and glamour and has been derided for pushing a discredited charge that Obama was not born in the United States. He has toyed with entering the presidential race himself, possibly as a third-party candidate. "This signifies a further consolidation of the Republican base," Republican strategist Ford O'Connell said. But, given Romney's comments yesterday, I could see (Obama's campaign) would like to tie this as a way to portray Mitt Romney as someone who is not in touch with the plight of the average American. The Democratic National Committee quickly seized the opportunity to release a video titled, "Mitt Romney and Donald Trump: They both like firing people," referring to the tagline of Trump's TV reality show "The Apprentice" and an earlier Romney gaffe, "I like being able to fire people." Trump said he was impressed with Romney's tough talk on China, India and OPEC. Romney criticizes China's trade policy frequently as he campaigns, and he lashed out again on Thursday. They've taken jobs from Americans. They haven't played fair. We have to have a president who will stand up to cheaters," Romney said. Trump announced he was leaving the Republican party in December after most of the Republican White House hopefuls, including Romney, declined to participate in a debate he planned to host. But from the Romney team's perspective it is better to have the casino and hotel owner with them than against them. Romney has won two of the first four contests in the state-by-state process of choosing a nominee, taking primaries in New Hampshire and Florida by healthy margins. Gingrich won South Carolina's primary, and former U.S. Senator Rick Santorum won Iowa's caucuses by a narrow margin over Romney. Romney seemed to snatch Trump's backing from Gingrich after U.S. media reported late on Wednesday he was supporting the former speaker of the U.S. House of Representatives, whose presidential campaign has been struggling since his upset victory over Romney in South Carolina on January 21. Gingrich hit Romney for his comments on the poor. I really believe that we should care about the very poor, unlike Governor Romney. But I believe we should care differently from President Obama," he said during a campaign stop at a Las Vegas manufacturing plant. What the poor need is a trampoline so they can spring up. I'm for replacing the safety net with a trampoline. A Fox News poll in January suggested support from Trump could do a candidate more harm than good. Twenty-seven percent of those surveyed said his endorsement would make them less likely to vote for a candidate. "It doesn't change my vote," said Sue Mathis, 52, of Las Vegas, who backs Gingrich. It means absolutely nothing. Trump is a good businessman, but a Steve Wynn endorsement would influence me more," she said, referring to the billionaire Las Vegas casino magnate. Romney won Nevada's caucuses easily during the 2008 campaign, thanks largely to support from his fellow Mormons, who account for about 25 percent of Republican caucus-goers. "The LDS (Mormon) thing cannot be understated in a Republican caucus," said David Damore, a political scientist at the University of Nevada, Las Vegas. They are obviously very energized. It's an opportunity to back one of their own. Additional reporting by Lily Kuo, Steve Holland and Patricia Zengerle in Washington, writing by Patricia Zengerle; editing by Mary Milliken and Cynthia Osterman