Updated 4:22 p.m. Eastern Time
LAS VEGAS, Nev. - Donald Trump said Thursday he's endorsing Mitt Romney because of his position on catching up to China's economic growth and because he believes Romney can out-debate President Obama.
"You look at what's going on with China, you look at what's going on with the other OPEC nations and how they are absolutely destroying this country, and he's the only one who talks about it," Trump told a group of reporters at an impromptu news conference in Las Vegas. "So that was very important to me. I thought he did very well in the debates, that was very important.... I think if he debates that well, I don't think Obama will fare well against him."
Romney's campaign formally unveiled the endorsement at an event in Las Vegas. Trump, who met with all the presidential contenders, said the former Massachusetts governor's campaign courted him "very aggressively."
At the event, Trump told the crowd: "Mitt is tough, he's smart, he's sharp, he's not going to allow bad things to continue to happen to this country that we all love...So Governor Romney, go out and get 'em, you can do it."
Romney, meanwhile, joked, "There are some things that you just can't imagine in your life; this is one of them." He described himself as "not quite as successful as this guy, but successful nonetheless."
Although multiple news reports on Wednesday night quoted anonymous sources as saying that the flamboyant real-estate tycoon and reality-show star would endorse Newt Gingrich, Trump said he never told anyone that he would back the former House speaker.
"They put that out," Trump told reporters, referring to Gingrich's campaign.
Trump said he intends to actively campaign on Romney's behalf, giving speeches that call attention to fixing the economy.
"I have a lot of people that like what I say," he said. "Look, I don't like seeing our country being ripped off. And that's what's happening. Every nation, no matter who it is, is ripping off this country. And it's gotta stop. So he sees that, and the other candidates see that, and I have a lot of people who agree with me."
Although Romney obviously hopes that Trump's support will help sway undecided voters, Democrats were quick to use the endorsement to make light of Trump's signature line, "You're fired!" and Romney's recent comment that he likes being able to fire people who provide him with subpar service.
"Why would Trump Endorse Romney?" blared the headline of a statement realeased by the Democratic National Committee. "Perhaps because they Both Like Firing People!
In addition, President Obama's spokesman Jay Carney made light of the endorsement at Thursday's White House press briefing.
Asked if the president sought Trump's endorsement, Carney said, "I'm not going to comb over that" -- a reference to Trump's celebrated hairstyle. After the laughs that followed, the press secretary added, "There's a danger in speaking off the cuff."
A reporter shot back: "You mean off the top of your head?" Then another added: "Jay, don't just brush this off."
Although Democrats have sought to make an issue of Romney's wealth as evidence that he cannot connect with average Americans, Trump said he thinks that won't be an issue.
"I think he's actually becoming very comfortable recently, more recently very comfortable with it," he said.