As nine candidates prepare to take their place alongside Donald Trump today for the first Republican presidential debate, a question looms: how does one deal with a rival whose bombast is part of his DNA? The property tycoon turned White House contender is also the most prolific political-insult generator in the US, imposing a sense of must-see-TV on the opening duel of the 2016 cycle.He blasted fellow Republican White House hopeful Jeb Bush as "weak", Senator Lindsey Graham as an "idiot", and former Texas governor Rick Perry as a buffoon who wears glasses "so people will think he's smart".Most controversially, he mocked the war hero status of US Senator John McCain of Arizona, the party's 2012 presidential candidate and a prisoner during the Vietnam War.Despite or perhaps because of his outrageous promises and harsh invective, the brash billionaire has snatched a wide poll lead. Trump, who described himself as ''a nice person'', said this week he was not planning to go on the offensive."I don't think I'm going to be throwing punches. I'm not looking to attack them ," he said.There is plenty for his party rivals to take aim at: Trump has in the past supported abortion rights and universal healthcare - heresy for the Republican base - and has backed Democrats like Hillary Clinton.But taking pot shots at Trump could trigger a response in kind.Graham, who branded Trump a "jackass", insisted the tycoon might make more sense to viewers if they were drunk.A veteran of primary debates, McCain recommended sobriety.But "I clearly would challenge some of his assertions", McCain said. "Prepare to discuss the issues."Carmine Gallo, a communications expert, warned those challenging The Donald: "Stay in your lane."You can't out-Trump Trump. Americans like their heroes to be authentic and you'll look like a phoney if you try to match someone else's personality."Candidates who cross into bullying behaviour risk a backlash from voters. In 2000 , Republican Rick Lazio interrupted fellow Senate candidate Clinton by walking to her podium, campaign finance pledge in hand, and urging her to sign it.A heated 2011 primary debate turned physical when a frustrated Mitt Romney, the eventual Republican nominee, placed his hand on Perry's shoulder.Trump shines when he faces the cameras alone. It might be different when he shares the stage."I actually predict that Mr Trump will be focused on policy and respectful," grinned Republican Senator Rob Portman, who played the role of President Barack Obama in Romney's 2012 debate prep. ..