At the upcoming presidential debate, Donald Trump will shine a spotlight on the fact that he’s not more mentally sharp than President Joe Biden, according to the former president’s biographer. Tim O’Brien, who spent massive amounts of time with Trump before writing TrumpNation: The Art of Being the Donald, appeared on MSNBC on Saturday where he was asked about Trump’s debate with Biden. Earlier this month, O’Brien undermined the ex-president’s claim that he wasn’t concerned about jail after being convicted on 34 counts. This weekend, O’Brien was asked about Trump reportedly preparing for the d…