He seemed to position himself in an unusual way, as a blunt truth-teller who is willing to blow up the established order but also a consummate insider who has donated millions of dollars to politicians in both parties, including some of his current rivals.
He even pointed to his own donations, and the favours that politicians have done for him in return, as an example of what's wrong.
"When they call, I give," he said. "They are there for me, and that's a broken system." He jabbed at some of his nearby hopefuls, at one point telling Kentucky Senator Rand Paul, "You're having a hard time tonight."
Trump asserted that his incendiary comments on illegal immigrants have revived the debate on border security rather than damaging the Republican brand. "If it weren't for me, you wouldn't even be talking about illegal immigration," he said. "This is not a subject that was on anyone's minds."
The scene, which was expected to draw record viewership for a primary debate largely because of Trump's presence, underscored two major developments this summer in the roiling battle for the Republican nomination.
For his part, Trump showed a longing to be seen as more than a rambling billionaire as well as some increased discipline since his June launch. His adversaries, meanwhile, seemed to acknowledge with their words and manner that, in a time of sprawling conservative unrest, Trump has become a force who is instinctively channelling the base's frustrations.
"Donald Trump is hitting a nerve in this country," said Ohio Governor John Kasich. He added: "For people who want to just tune him out, they're making a mistake."
Another rival, former Silicon Valley executive Carly Fiorina, said in an earlier debate among the lower-tier candidates that Trump has "tapped into an anger that people feel".
On his rough experience in struggling Atlantic City, Trump took aim at New Jersey Governor Chris Christie. "Chris can tell you" all about the seaside city's economic downturn, Trump said. "I had the good sense and I've gotten a lot of credit in the financial pages, seven years ago I left Atlantic City before it totally cratered," Trump said. "And I made a lot of money in Atlantic City, and I'm very proud of it."
In one exchange of the type that would cause a normal politician to cower - and likely bury his campaign - Fox News' Kelly asked Trump about numerous insulting and disparaging statements he has made about women. Trump was not bothered in the least about this line of questioning. In fact, he encouraged it.
"You've called women you don't like 'fat pigs, dogs, slobs, and disgusting animals'," Kelly said. "Only Rosie O'Donnell," replied Trump, drawing laughter from the crowd.
"For the record, it was well beyond Rosie O'Donnell," Kelly persisted.
"Yes, I'm sure it was," Trump agreed, drawing more laughs.
Trump offered a few kind words for former Florida Governor Jeb Bush, calling him a "gentleman". But when Bush expressed concern about Trump's immigration rhetoric, saying the GOP should offer a more hopeful message, Trump responded that, in a hostile world, "we don't have time for tone".
One of the loudest rounds of applause on the night was for Marco Rubio when he mocked Hillary Clinton, who leads the Democratic field.
"First let me say, I think God has blessed us. He's blessed the Republican Party with some very good candidates. The Democrats can't even find one."
