The top contenders all have the potential to be their own worst enemy when they take the stage in Cleveland -- not due to Trump's bombastic style but because of their own quirky qualities. Those traits can be assets or liabilities as the candidates struggle for the spotlight in the unwieldy GOP field.
Here's a look at what the top Republican candidates need to remember not to do as they try to survive -- or win -- this first debate round.
Marco Rubio -- The Florida senator is always in a hurry, so much so that when he turned 45 years old earlier this year, he said he felt like 46. His quick wit has been an asset -- joking during a foreign policy interview that if Cuban leader Raul Castro is considering a return to Catholicism, it's going to require a long confessional. But that sharp tongue can also make the youthful-looking Rubio, who confesses being a "brat" as a child, appear less mature for commander-in-chief.
Ted Cruz -- The brainy Texas senator needs to remember this is live TV, not a conservative legal argument he might have made before the Supreme Court in a past profession. No filibustering allowed.
And then there's Donald Trump. The billionaire is expected to dominate the debate, and in doing so he mainly needs to remember that this is not a reality show, but a chance to become the leader of the free world. Act accordingly.
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