AIKEN, South Carolina -- Donald Trump was on his way to the Mexican border Thursday, the latest event in a presidential campaign some of his Republican rivals would like to dismiss as a sideshow -- a “carnival act,” as one puts it.

But the billionaire developer and reality TV host has been stealing their thunder for days and left them scrambling to adjust to a race dominated by a bombastic longshot.

From party heavyweights like Jeb Bush to recently announced candidates like Wisconsin Gov. Scott Walker and Ohio Gov. John Kasich, the contenders are confronted by Trump‘s hair-trigger habit of calling out his critics by name, vilifying the Republican establishment and roiling the debate over immigration and more.

Trump was to hold a news conference at the U.S-Mexico border, meet members of the union that represents Border Control agents and speak to law enforcement officers, his campaign said. The border became a flashpoint in the Republican debate when Trump branded Mexican immigrants rapists and drug-bearing criminals.

After that episode came a broadside against Sen. John McCain, who earned Trump’s ire by saying his remarks about immigrants had brought out “crazies.”

Trump mocked McCain‘s experience in the Vietnam War where he was tortured as a prisoner, called him “dumb” and laced into his record on veterans’ issues in the Senate.

In Washington, former Texas Gov. Rick Perry was asked about Trump‘s planned trip to the border. He snapped, “I hope he can find the border because I’m not sure he‘s ever been there before.”
 

This, after Perry denounced Trump’s campaign as a “cancer on conservatism” and “barking carnival act” in a speech that laced into “Trumpism: a toxic mix of demagoguery, mean-spiritedness and nonsense that will lead the Republican Party to perdition if pursued.”

Indeed, the insults flying between Trump and his fiercest critics have been caustic. Sen. Lindsey Graham called him a “jackass” a day earlier and Trump responded by calling Graham an “idiot” and giving out the senator‘s cell phone number, jamming his voice mail.

Others in the field have been more measured, though showing signs of growing exasperation. Bush, in particular, has conspicuously tried to avoid alienating Trump’s supporters -- “good people” with “legitimate concerns” -- even while branding Trumps‘ rhetoric “ugly” and “mean-spirited.”

The feud is unfolding as the candidates prepare for the first Republican debate, a venue to which the top 10 in national polling will be invited out of a swollen lineup of 16. Although they are all accomplished, few are well known nationally, and “Trumpism” isn’t making it easier for them to get their messages out at a time when mere name recognition can drive popularity in polling.

Trump, a longtime celebrity, is almost guaranteed a spot in the debate.

Bush, in South Carolina on Wednesday, said he wasn‘t approaching the debate thinking about Trump or any rival who might be on the stage. “My objective with this is to, wherever I can, share my record,” he said.

Sen. Rand Paul, a day earlier, addressed the Trump feud almost serenely, expressing confidence the primary campaign would “get beyond the novelty of a reality TV star.”

And Walker, campaigning in Tennessee, said he used to run track and “I realized there were some folks sprinting out ahead. I made sure I was ahead at the end of the race when it really mattered.”

Trump remains unbowed. “I’m called a jackass,” he said Wednesday on CNN. “You have to fight back. The country has to fight back. Everyone‘s pushing our country around. We can’t allow that.”

Meanwhile, federal regulators made public records that show, as he has said, that he is rich.

He has assets of at least $1.4 billion and debt of at least $240 million, the regulators said in a report with such broad categories that his wealth could well be much greater. His precise fortune isn‘t pinpointed, but the disclosures underscore his financial potential staying power in the race and his freedom from the influence -- or muzzles -- of the deep-pocketed Republicans who bankroll rival campaigns. (AP)