Hillary ClintonHillary Diane Rodham ClintonDemocrats worry negative images are defining White House Heller won't say if Biden won election Whitmer trailing GOP challenger by 6 points in Michigan governor race: poll MORE's campaign manager, Robby Mook, said they still haven't found a person to play Donald TrumpDonald TrumpGraham says he hopes that Trump runs again Trump says Stacey Abrams 'might be better than existing governor' Kemp Executive privilege fight poses hurdles for Trump MORE in mock presidential debates.

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"It's very hard to find someone to mimic the reckless temperament and the hateful instincts and divisive instincts of Donald Trump," Mook said Sunday on CNN's "State of the Union."

"Preparing for a debate with him is a challenging task, but Secretary Clinton is looking forward to the debate."

Mook said he expects the public will see a stark difference between "steady leadership" and a "very reckless temperament" during the presidential debates.

Clinton, the Democratic presidential nominee, has been "in this game" for a long time, he said, noting that she's had a lot of "tough things" said to her.

The challenge in this situation is finding someone able to recreate the Republican presidential nominee's divisive and hateful rhetoric, Mook said.

But he said he's confident the campaign will find someone.

"We'll get it done," he said.

"We're looking forward to the debates."