Mitt Romney - Trump Endorses Romney

NEW:Trump said he previously criticized Romney before getting to know him

The value of a Donald Trump endorsement of Mitt Romney is unclear

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The Republican candidates are campaigning in Nevada, which holds its caucuses Saturday

(CNN) Celebrity business magnate Donald Trump endorsed Mitt Romney for president Thursday, telling reporters he will not mount an independent campaign if Romney is the Republican nominee.

Trump, who has repeatedly flirted with the possibility of his own White House bid, revealed his decision in Las Vegas two days before Nevada's Saturday caucuses.

"It's my honor, real honor, to endorse Mitt Romney," Trump said, with Romney and his wife standing nearby. Calling Romney "tough" and "smart," Trump said, "he's not going to continue to allow bad things to happen to this country."

Romney responded by praising Trump for "an extraordinary ability to understand how our economy works and to create jobs" and for being "one of the few who has stood up to say China is cheating" in international trade.

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."

Trump was not always so positive regarding Romney's record. During an interview on CNN's "State of the Union" in April, Trump criticized Romney for eliminating jobs while in the private sector.

"He'd buy companies. He'd close companies. He'd get rid of jobs," Trump told CNN Chief Political Correspondent Candy Crowley. "I've built a great company. My net worth is many many times Mitt Romney."

Asked what changed since then to bring his endorsement of Romney, Trump told CNN later Thursday that his past comments were "political talk."

"That was a long time prior to my getting to know him," Trump said of Romney. "But I have gotten to know him and he's a terrific guy. I don't know if he really comes out like he really is in person. He's a warm, smart, tough cookie and that's what this country needs. We need somebody that's tough, that will stop China and OPEC and all these other nations from just ripping us up. And i think he can do it."

CNN's Tom Cohen, Jim Acosta, Paul Steinhauser and Alyssa McLendon contributed to this report.