The most pressing question that Donald J. Trump could face next week in the first debate of the 2016 presidential race may not be about Iran or immigration, but this: Can he deploy enough adjectives (“huge!”), superlatives (“the worst!”) and invectives (“loser!”) for him to use up his time without being challenged successfully on the substance of policy?

Mr. Trump could come away a winner if he makes cogent points without sounding too hostile, presenting himself as more of a serious-minded, anti-establishment voice in a primary crowded with career Republican politicians. But there are risks for him if he turns the debate stage in Cleveland into another episode of the reality show his campaign has sometimes resembled.

He boasts about spending no time preparing for the event, which will be broadcast on Fox News on Aug. 6, even as his aides have put together briefing papers for him on policy and pungent lines of attack. He already knows plenty about the issues, he says, so much that, rather than cramming, he will be in Scotland over the weekend at a golf tournament on one of his courses.

And after weeks of slashing at his opponents in interviews, he refuses to say whom he may single out when the 10 leading primary contenders stand side by side. “I have great respect for some of the candidates,” Mr. Trump said in an interview. “I don’t have great respect for others.”