Donald Trump was expected to endorse Newt Gingrich, while Mitt Romney predicted the White House race would be one of the nastiest in U.S. history.
Trump -- the New York business magnate, TV personality and author -- was expected to make the Gingrich endorsement at a 12:30 p.m. PST news conference in Las Vegas at Trump International Hotel & Tower, KLAS-TV, Las Vegas, and Politico reported.
Trump said this week he might run a third-party campaign if he didn't see a Republican candidate he thought could beat President Barack Obama. Trump first said last year he might run for the White House, but said later he wouldn't, after attacking Obama over the validity of his birth certificate.
Gingrich, a former U.S. House speaker, told reporters in Reno, Nev., Wednesday he was unaware of Trump's plans.
Romney, a former Massachusetts governor, created a stir Wednesday when he told CNN he was "not concerned about the very poor."
"I'm in this race because I care about Americans," he told CNN in an interview. "I'm not concerned about the very poor. We have a safety net there. 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 percent, 95 percent of Americans right now who are struggling and I'll continue to take that message across the nation."
Romney, whose net worth is estimated at more than $200 million, cited food stamps, housing vouchers and other benefits in explaining his comment on concern for the poor.
Gingrich quickly picked up on Romney's comment.
"I am fed up with politicians of either party dividing Americans against each other," he said. "I am running to be the president of all the American people, and I am concerned about all the American people."
Romney told ABC News he expected the campaign against Obama would be the bitterest and nastiest in U.S. history.
"No question that Barack Obama's billion-dollar machine will organize the most vitriolic, spiteful campaign in American history," he said. "We have to be ready for that."
Romney starts receiving Secret Service protection Thursday.
Former Sen. Rick Santorum of Pennsylvania campaigned in Colorado while Rep. Ron Paul of Texas was in Nevada.
Several states hold GOP caucuses starting in two days. Nevada's will be Saturday and the Maine caucuses run from Saturday through Feb. 10, followed by the Colorado and Minnesota caucuses Tuesday.
After those contests, the nominating calendar has a three-week lull until Michigan and Arizona vote Feb. 28.
