NEW YORK — Since he entered the presidential race, it’s been Donald Trump’s style to break with convention. It’s no different when it comes to debate prep.

The New York billionaire has skipped practicing a full debate as he gets ready for his first on-stage meeting with Hillary Clinton. While he has studied policy ideas and practiced answering questions he may face Monday night, experts who have been through the process call his decision to skip time-intensive mock debates a mistake.

“I think he’s putting himself at an incredible disadvantage,” said Brett O’Donnell, a Republican strategist and veteran debate coach who compared Trump’s decision to a football team failing to scrimmage.

Trump’s Democratic rival, Hillary Clinton, has run through full-length mock debates against a stand-in for Trump during her preparation sessions. For good reason, O’Donnell said. Gaming out every potential permutation of what might happen in the 90-minute showdown helps a candidate calculate how to respond.

“If you simulate what could happen in the debates, then you understand how to handle those moments when they actually do happen,” he said.

Trump’s approach couldn’t be more different than the one pursued in 2012 by Republican nominee Mitt Romney, who started holding practice debates in late August — more than a month before the first general election debate.

His preparations were meticulous: The practice podiums were built to match those he would find on the debate stage and the mock debates were precisely timed. Later rehearsals were held in hotels across the country as he campaigned, with Ohio Sen. Rob Portman playing the part of President Barack Obama.

In all, Romney held 16 mock debates and arrived in Denver, the site of his first meeting with Obama, several days in advance for final run-throughs and even to prepare for the host city’s altitude. He won high marks in the opening debate against a lackluster Obama, who picked up his game in later debates.

Former Michigan Gov. Jennifer Granholm, who played then-Alaska Gov. Sarah Palin in mock debates against Vice President Joe Biden in 2008, described such sessions as “absolutely crucial.”

Granholm said Biden’s mock sessions aimed to “replicate the circumstances as close to the real thing as possible,” with the stand-in and candidate testing out different approaches to the debate.

That includes practicing for the added challenge of debating a woman. Research has shown that a combative debating style can backfire when it’s used against female opponents, especially among women who are watching, said Dianne Bystrom, director of the Carrie Chapman Catt Center for Women and Politics at Iowa State University.

Granholm said that Biden’s advisers were acutely aware of that as they prepared to take on Palin, and he practiced to make sure he never came across as paternalistic or lecturing.

“There’s a slice of the voters who are very sensitive about a man appearing to bully a woman,” Granholm said. “So whether it’s in your physical space or verbally, I think it sets off alarms bells and it’s something that Donald Trump has to worry about.”

Trump’s advisers have coached the celebrity businessman to resist attempts by Clinton to provoke him with questions about his business record, wealth or contentious comments about minorities, including his fabricated theories about where Obama was born.

But former House Speaker Newt Gingrich, who is part of a rotating cast of advisers helping the Republican nominee get ready for the debates, said there’s also a risk of coaching Trump too much.

“His instincts are so different than everyone else’s that I think trying to coach him will screw him up,” Gingrich said. “He won every debate he was in by saying things no one else would. Don’t mess with that.”

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