2016 GOP Presidential Debate: Donald Trump Preps to Take Center Stage

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Thursday's GOP presidential debate will feature five governors, three senators and a former brain surgeon, but most viewers will be tuning in for the billionaire from New York.

ET has learned that Donald Trump's wife Milania, his daughter Ivanka and son Eric, along with the rest of the Trump family, have made the trip to Cleveland for the patriarch's first debate. Insiders are reportedly concerned that Trump will hog the spotlight, running over his time limits, breaking rules and taking control.

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"I think he'll try to be presidential," Rob Lowe told ET. "Here's the thing, he's on TV every week. This is nothing for the Donald. He's the last person to worry about."

Despite his lack of political experience in comparison to some of his rivals, Trump sits atop most GOP polls. What's more, Trump has been known to provoke his enemies. The real estate magnate showed no mercy to Rosie O'Donnell in 2006 after she called him a "snake-oil salesman."

"It's not the chubbiness. Rosie is a very unattractive person both inside and out," Trump told ET at the time. "If I were running The View, I'd fire Rosie. I'd look her right in that fat, ugly face of hers and I'd say, 'Rosie, you're fired.'"

Trump has stated that he wants to stick to the issues during tonight's debate, but won't back down from a fight.

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"If I'm attacked, I have to do something back," Trump said on ABC's Good Morning America. "But I'd like it to be very civil."

Trump will be joined by Jeb Bush, Scott Walker, Mike Huckabee, Ben Carson, Ted Cruz, Marco Rubio, Rand Paul, Chris Christie and John Kasich.