He slammed Democrat frontrunner Hillary Clinton, as "the worst secretary of state in the history of our country" and said: "She's going to be beaten and I'm the one to beat her."
Some Americans are amused. Others are horrified. A swathe of ordinary voters, fed up with Washington DC, say he speaks for them and cable television networks follow his every move.
Retired basketball star Dennis Rodman, known for visiting North Korea and for his flamboyant dress sense, on Friday appeared to endorse the mogul with the blonde comb-over for the White House.
"@realDonaldTrump has been a great friend for many years. We don't need another politician, we need a businessman like Mr trump! Trump 2016," (sic) he tweeted to his half a million followers.
And he closed yet another working week as king of the polls.
The latest survey released by YouGov on Friday put Trump on 28 per cent, streets ahead of nearest Republican rival, Wisconsin governor Scott Walker on 13 per cent, among party voters.
Trump's brazen remarks and outlandish stunts leave little space for the more carefully calibrated points made by other candidates, Republican or Democrat. It is Trump, Trump, Trump.
"Donald Trump is sucking the oxygen out of the room for everybody else," Stuart Rothenberg, founder of the Rothenberg and Gonzales Political Report, told NBC News.
On Thursday, CNN broadcast live his arrival - by private jet emblazoned with his name in huge golden letters - at the Texas-Mexico border to condemn illegal immigration and declare his love for Latinos.
By contrast, when Ohio Governor John Kasich announced his candidacy, he was almost ignored.
A video produced by fellow candidate Republican Senator Rand Paul showing him setting America's 70,000-page tax code on fire also panned: a vain attempt to wrest back some publicity.
Republicans, their noses out of joint, don't know how to fend off such an unpredictable, and populist opponent.
"That's what the serious campaigns are trying to figure out," NBC political director Chuck Todd said.
"They are worried that the more they attack and marginalise him, the stronger he gets."
The man nicknamed "The Donald" who claims to be worth more than US$10 billion (A$13.60 billion) is self-financing his campaign and appears to be revelling in the attention.
The most feted political satirist in contemporary America, Jon Stewart, who next month steps down as anchor of The Daily Show has pored over Trump night after night.
"Thank you, Donald Trump," he said "for making my last six weeks ... my best six weeks."
Some Republicans already fear the tone of their debate, scheduled on August 6, to which the top 10-poll ranking candidates are invited.
But political strategists may be able to sleep in peace: in the YouGov poll, only 10 per cent of registered voters who identify as Republican thought he would win the party's nomination.
A whopping 36 per cent thought that honour would go to Jeb Bush, the former governor of Florida who is the son of one former president and the brother of another.
- AAP
