Donald Trump says “millions of people” are waiting for his endorsement in the race for the Republican nominee for president ahead of next year’s election. (Spencer Platt/GETTY IMAGES)

To hear Donald Trump tell it, “millions of people” are waiting for him to make an endorsement in the Republican presidential primary. And at some point, he says, he’ll likely grace a candidate with one — that is, unless he decides to run himself as an independent.

The real estate mogul and reality TV star, who flirted with seeking the Republican presidential nomination but decided to sit out, says he has a “tremendous following of people who are tired of seeing this country get ripped off.”

“Everybody wants it,” Trump, referring to his endorsement, said in a phone interview. “I have millions of people waiting for me to do it.”

Trump’s outsize confidence in himself as both kingmaker and potential king should make any serious presidential candidate wary of being endorsed by him, some political scientists say.

Yet during the past few months, Rick Perry, Newt Gingrich and Mitt Romney have made the journey to Trump’s headquarters in New York to seek the The Donald’s blessing.

Even though research shows most endorsements are of limited value to a candidate’s electoral fortunes, office seekers continue to chase them. They tout them in campaign ads and show off their trophy backers at events and news conferences.

But while the support of organizations such as labor unions might translate into money, volunteers and actual votes, University of Virginia political science professor Larry Sabato says, “the vast majority of individual endorsements are worth the vote of the endorser and, about half the time, the endorser’s spouse.”

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Romney, who for much of the year has struggled in the polls, is far ahead in the endorsement derby, having racked up several pledges from high-profile Republicans — including tea party favorites South Carolina Gov. Nikki Haley and Delaware senatorial candidate Christine O’Donnell. Meanwhile, for much of the year his frontrunner status has been challenged by a rotating cast of anti-establishment candidates favored by rank-and-file Republicans. A Washington Post-ABC News poll published Dec. 20 showed that, nationally, Romney was tied with Gingrich, with each favored by 30 percent of Republicans and Republican-leaning independents.

“Governor Romney is proud to have the support of a growing number of strong conservative leaders, from Governor Nikki Haley and Governor Chris Christie to important primary state publications such as the Des Moines Register and Portsmouth Herald,” Andrea Saul, the campaign spokeswoman, said in an e-mail.

Gingrich, a former U.S. House speaker, has gotten the endorsements of the state house speakers of Iowa and New Hampshire, the first two primary states, and he has also been tapped by the Manchester Union-Leader in New Hampshire.

John Huntsman has touted the endorsement of Jeb Bush Jr., son of the former Florida governor, nephew of the 43rd president and grandson of the 41st. Rep. Michele Bachmann’s most famous backer so far is conservative activist Phyllis Schlafly. Ron Paul has touted the endorsement of actor Vince Vaughn and the student newspaper at the University of Iowa, the Daily Iowan.

Kathleen Hall Jamieson, director of the Annenberg Public Policy Center at the University of Pennsylvania, recently co-wrote an article arguing that the Union-Leader’s endorsement of Gingrich has the effect of “certifying” him as “a kindred conservative spirit” while suggesting that Romney is not. She calls this the “push-pull” phenomenon of endorsements, noting that in 2008 the New York Times endorsement of John McCain might have endeared him to moderates but radio personality Rush Limbaugh repeatedly invoked it to persuade his listeners to challenge the Arizona senator’s conservative creds.

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In early elections of the new United States, presidential candidates did not actively campaign for office, leaving the politicking to friends and party activists.

Sabato cited the 1908 presidential election, in which Theodore Roosevelt pushed William Howard Taft as his successor, as a “clear historical marker” for when endorsements began to matter. That year, the Web site of the AFL-CIO notes, the AFL endorsed Democrat William Jennings Bryan for president.)

The popular of celebrity endorsements gained momentum with John F. Kennedy’s first presidential campaign.

“The Kennedy campaign in 1960 is often referred to as the Hollywood campaign,” Sabato said. “Never had so many Hollywood stars gathered around a candidate for president like they did for Kennedy.” Frank Sinatra organized events for the candidate and even sang the campaign theme song, an adaptation of the song “High Hopes” — “Which was a hit!” Sabato added.

In general, most Americans say endorsements are not important to them in deciding whom to support for president. In a 2007 Gallup poll, the latest numbers on the subject, 61 percent said endorsements from “prominent people” are not important to their decisions, while 37 percent said they were important, including 16 percent who said they were very important. Democrats were somewhat more likely to say endorsements mattered.

Endorsements from celebrities, such as Trump, appear even less critical. In a 2007 Washington Post-ABC News poll, nearly nine in 10 Americans said candidate endorsements from entertainment figures or celebrities made only a little difference or none at all; 11 percent said they mattered a great amount or a good deal.

Ron Lester, a Democratic pollster, said endorsements work “cumulatively,” creating buzz and news coverage for a candidate and giving the appearance of broad support.

“In a campaign every time you put points on the board it’s important, so endorsements add up cumulatively,” he said.

Endorsements are worth more in primaries because they give voters cues about candidates’ ideological standing. Both Jamieson and Sabato cited the endorsements of Caroline Kennedy and her uncle, the late Sen. Ted Kennedy, as having passed the liberal torch to Barack Obama at a time when Hillary Clinton was threatening to overtake him in the 2008 Democratic presidential primary.

For the current GOP primary, Sabato said a nod from former Alaska governor Sarah Palin could be helpful because of her popularity with conservative activists — she has said she doesn’t plan to endorse anyone — but would likely turn off swing voters in a general election. Georgia businessman Herman Cain, who dropped out last month after allegations of an extramarital affair, has said he would endorse a contender, and Sabato said it could swing a few votes toward the chosen candidate.

“His true believers would seriously consider moving to someone he’s endorsed. Based on what I’ve seen on Twitter and e-mail, there are still people saying, ‘He was railroaded right out of the race!’ But that’s a handful of votes, not tens of thousands.”

Late last week, Trump changed his party registration to unaffiliated.

“Mr. Trump did this in order to preserve his right to run in the 2012 presidential race if he is not satisfied with who the Republican nominee is,” Michael D. Cohen, a spokesman for Trump, said Tuesday. He said Trump will make decision his “sometime prior to the finale of ‘The Apprentice,’ around the first week of June in 2012.”

In the meantime, Jamieson is not sure why any candidate would court an endorsement from Trump.

“His embrace of the birther issue made him look bad. His flamboyance is not an asset,” Jamieson said.

The numbers also suggest that a Trump endorsement would not be very helpful and might even be harmful. In a Fox News poll in September, 71 percent of Republicans said it wouldn’t matter in their vote, 18 percent said it would make them less likely to support the candidate and 10 percent said they’d be more likely to vote for the endorsed candidate. Among the general public overall, Trump’s endorsement was seen as a net negative 31 percent to 6 percent, again with the overwhelming majority saying it made no difference (62 percent).

Still, Gingrich gleefully said he wanted Trump’s endorsement and was one of only two of the six GOP contenders to accept an invitation to a Trump-sponsored debate before the Iowa caucuses. The event was canceled after it became clear that Trump was still mulling a run himself. Romney did not talk to reporters after a September meeting with Trump, and his campaign did not respond to questions about whether he still wanted the endorsement.

In a phone interview, Trump, of course, disagreed that his endorsement would be harmful. Those millions are waiting to know what he thinks. “We all know that,” he said, “whether it’s my views on China and OPEC and the world ripping us off and other issues.”

Like the birther issue? “Everything, including the birther issue,” Trump said. “Many people out there are not convinced — in their minds, this has not been solved — but are more interested, however, in seeing that this country has jobs and isn’t ripped off by virtually every other country it does business with.”

“I will be probably making an endorsement,” he said. “And I’m not in a rush to do it.”

Polling analyst Scott Clement and researcher Madonna Liebling contributed to this report.