And yet, Trump is running a strong second to former Massachusetts Gov. Mitt Romney in most recent beauty-contest polls of likely GOP voters. (Trump boasts that he's "leading all the polls," but that's just another Trumpism.)
"It means this Republican nomination is still wide open — as wide open as any we've ever seen," said Scott Reed, who managed Bob Dole's unsuccessful 1996 campaign.
Less politely, it means that none of the potential candidates now testing the waters — Romney, former House Speaker Newt Gingrich, former Minnesota Gov. Tim Pawlenty and Mississippi Gov. Haley Barbour, to name the most prominent — has caught fire yet. The GOP voters who told pollsters they would favor Trump listened to that list of names and replied, in effect, "none of the above."
Moreover, a look at the poll numbers shows that Trump's support comes at the expense of potential candidates whose standing has eroded in recent months: former Alaska Gov. Sarah Palin, former Arkansas Gov. Mike Huckabee and Gingrich.
So the GOP race is becoming more open, not less.
But that's not all the Trump mini-surge portends. As last November's congressional election showed, there's a deep wellspring of anger and impatience in the electorate. Much of it found expression in the "tea party" movement of fiscal conservatives, but the phenomenon is broader than that.
Just as in 2008, when then-candidate Obama promised to change the way Washington works, many voters want a candidate who can credibly promise fundamental reform — and they haven't found a champion yet.
"People are looking for a new dimension that goes beyond conventional politics," said Eddie Mahe Jr., a former vice chairman of the Republican National Committee. "They're looking for a leader who's going to change things, who can overcome the special interests and pull people together around a common agenda. Trump offers some of that quality." (He's not a Trump supporter.)
Where does that leave the Republican race?
It leaves Romney as a putative front-runner whose support appears frozen at about 1 in 5 GOP voters; his share in the polls has neither grown nor shrunk in recent months.
It also leaves Romney in an uncomfortable position as the most moderate conservative in the Republican field, open to charges from his rivals that he's not conservative enough. Some Romney supporters are privately rooting for former Utah Gov. Jon Huntsman Jr. to join the race, if only to add a name to Romney's left.
On the right, Pawlenty is trying to cast himself as a candidate for tea party supporters; he has demanded that Congress refuse to raise the federal debt ceiling under any circumstances, even though House Republican leaders have said they are willing to seek a compromise on the issue.
But Pawlenty's strategy may not succeed if a real tea party candidate, such as Rep. Michele Bachmann (R-Minn.), enters the race.
The gap between Romney and the tea party types is a space that might be tailor-made for Barbour, a Southern conservative who can point to a successful record as Mississippi's governor, including his management of the state's response to Hurricane Katrina in 2005.
But Barbour faces a paradox: As a former Washington lobbyist and Republican fundraiser, will his solid qualifications as a professional politician disqualify him in a year when conventional politics is so out of fashion?
So far, none of those names, except perhaps Bachmann, has produced much passion in Republican ranks — and Bachmann produces passion both for and against.
But that's not unusual at this stage of a presidential campaign. Candidates who look weak at the outset quickly can gain stature if they begin to win primary elections. The first real contest, in Iowa, is still eight months away.
"One of these Republicans is going to rise out of the water," Reed promised. "Somebody will look presidential."
Indeed, most Republican strategists think any of the current or former governors in the mix — Romney, Pawlenty or Barbour — could pose a credible threat to Obama.
When a president runs for a second term, they noted, the election is primarily a referendum on how he did the job. The identity of the challenger isn't as important as the unemployment rate, the price of gasoline or the president's job approval rating.
This is all good news for the GOP, so far. The president's job approval rating, for example, stands at about 48%, which means if the election were held today, it would end roughly in a tie.
So Republicans can stop wringing their hands in public and private over who will be their flag-bearer. A nominee will emerge, and it won't be Donald Trump. Besides, the other side expects a close race. Obama already opened his campaign, and he is running hard.