Jon Stewart 's latest volley at President Donald Trump focused on the president's constant boasting about his cognitive health – and resurrected an old clip of an embarrassing math fail to undermine his claims. Trump, who turns 80 next month , has been insistent that he is still perfectly healthy , both in body and mind. He has claimed on numerous occasions that he has "aced" multiple cognitive tests and is sharper than any previous president. “I took three cognitive tests. Aced all of them, by the way. ... I don’t think Obama could pass it,” Trump said on Friday during a press conference. But he wasn't done. On Monday, Trump continued to tout his clarity of mind. “No president has ever taken a cognitive test except me," Trump said.…