Presidential candidate Donald Trump talks to protesters as he leaves the World Trade Bridge border crossing in Laredo, Texas, July 23, 2015.
Presidential candidate Donald Trump talks to protesters as he leaves the World Trade Bridge border crossing in Laredo, Texas, July 23, 2015.

NEWARK, NEW JERSEY - They have been holding mock debates, hunkering down with advisers and finessing policy answers. But the most pressing concern for many Republican presidential contenders as they prepare for the first debate of the primary season in the 2016 election is one man: Donald Trump.

The billionaire businessman has dominated the Republican race in recent weeks, and he threatens to do the same when the top 10 Republican candidates – as determined by national polls – face each other for the first time on national television on Aug. 6.

It's a high-risk, high-reward event for candidates eager to stand out in a packed field in which Trump is playing the ultimate wildcard.

"It's the No. 1 unavoidability," said former House of Representatives Speaker Newt Gingrich, a 2012 Republican candidate who had a knack for standing out in debates four years ago.

Rivals warned

"Do not try to match him in anger and in aggressiveness. It's not possible," Gingrich warned Trump's rivals. "He's a very instinctively aggressive guy and if you try to dance with him on his strengths, he'll run over you."

Indeed, despite his longshot status, the reality television star has commanded attention and seen his poll numbers rise after firing off provocative comments about immigrants, his presidential rivals and critics in both parties.

His supporters love him because he's willing to say what others only think.

But that makes him dangerous in a debate setting, says Charlie Black, a leading Republican strategist who has worked on multiple presidential campaigns.

"Just try to ignore him," Black said. "The less attention you give him the better. I wouldn't even look at him."

Count former Texas Governor Rick Perry as among the candidates eager for a showdown, although he may not qualify for the debate in Cleveland, Ohio.

'Push back hard'

Only the top 10 candidates in national polling will be allowed on stage. With 16 declared candidates, several high-profile Republicans will be left out. Perry is on the bubble.

"If Donald Trump wants to sit on the stage and talk about solutions, I'm going to be happy to have that conversation," Perry said on Fox News. "But if all he's going to do is throw invectives, then I'm going to push back and I'm going to push back hard."

Even without Trump's emergence, the first debate promises to be an unruly affair.

In a 90-minute debate featuring so many candidates, there could be only enough time for four or five questions – with little time left over for the interaction between candidates that makes for an actual debate.

And few campaigns expect Trump to respect the time limits or other rules established by organizers.