WASHINGTON - Michael Mathes - Donald Trump steamrolls into Alabama for potentially the biggest US campaign rally of the year Friday, leaving Republican rivals flummoxed over how to contain the political brute now turning the presidential race on its head.

The billionaire real estate mogul has snatched the lion's share of the attention, interest and support of Republican voters, using a combative tone to lash out at other candidates with a coarseness rarely seen at the top tier of American campaigns.

With more than five months before Iowa and New Hampshire cast the early votes in the party nominating process, Trump leads in polls across the board, leaving the remaining 16 Republican candidates in his dust. He is a wildly hyperbolic, hugely entertaining non-politician -- and his anti-establishment clarion call has quickly become the loudest voice in US politics.

Trump has jetted into the heartland to attend the Iowa State Fair and stalked former Florida governor Jeb Bush in New Hampshire this week, where he bashed Bush's Iraq and immigration positions and ridiculed his floundering poll numbers. Now he is taking the Trump typhoon into the deep South, where outsized demand for tickets led organizers to upgrade Friday's venue from a theater to a larger arena and ultimately to a 43,000-seat American football stadium in Mobile, Alabama.

Trump predicted as many as 40,000 people would show up, which would be a record for the 2016 campaign so far, surpassing the 28,000 who showed up in Portland, Oregon two weeks ago to see liberal Senator Bernie Sanders, who is challenging Hillary Clinton for the Democratic nomination.

"We are going to have a wild time in Alabama tonight!" Trump blared on Twitter. His extraordinary early success has Republican candidates, donors and party leaders mystified.

"No one has figured out how to handle Trump," former New Jersey governor Thomas Kean, a Republican, told The Washington Post. "Everyone underestimated him terribly from day one. But as someone who knows him and knew his father -- the whole family -- I can assure you, that was a mistake."

Perhaps recognizing a need to counter the Trump machine, Bush has upped his rhetoric, snapping on Wednesday that Trump has "been a Democrat longer than being a Republican" and citing the magnate's earlier support for abortion rights and a single-payer health care system. Other candidates have gone after Trump head on, with little to show for it.

Senator Rand Paul berated him in an August 6 debate but it did minimal damage, and the Kentucky insurgent has slipped in the polls. Paul has also released an ad attacking The Donald, but that, too, has not moved the needle. And while rivals strategize over how to bump Trump, he continues to throw elbows. His latest target: low-polling Democrat Martin O'Malley, whom Trump called a "disgusting, little, weak, pathetic baby."

Meanwhile, Trump grows in stature, despite pundits and analysts forecasting that The Donald would be merely a passing political fad. "It's like a science fiction film, where you shoot at him and he gets bigger," Newt Gingrich, the former US House speaker who ran for president in 2012 and, like Trump, was an early frontrunner, told Fox News this week.

"You're dealing with somebody who is totally different from anybody in modern politics." Former New York governor George Pataki has offered some of the harshest condemnation, blasting Trumpism as "demagoguery."

But Pataki's is a voice from the back of the pack and it does not appear to be resonating. Mega-donors supporting other candidates are said to be mulling autumn ad runs attacking Trump. But they -- and candidates like Senator Ted Cruz and New Jersey Governor Chris Christie -- are treading carefully, hesitant to antagonize a political barbarian at the gates.

Meanwhile Trump generates enthusiasm rivals can only envy. New Hampshire state Representative Werner Horn, co-chair of a Veterans for Trump group there, said Trump is more than qualified to transform from blustery frontrunner to plausible nominee because he has decades of experience leading his industry and will do what it takes to avoid finishing second. "He wants America to be a winner," Horn said. "That's the mindset I want from the next commander in chief."–AFP