Joe Biden has been cast as a senile old man by President Donald Trump, but the challenger, 77, warned the incumbent, 74, not to underestimate his mental faculties Sunday. “Watch me, Mr. President,” Biden said in an interview with ABC News when asked about the president’s attacks on his cognitive ability. “Watch me. Look at us both, what we say, what we do, what we control, what we know, what kind of shape we’re in,” Biden added. If elected, Biden would be the oldest U.S. president ever. Trump, now 74, is the oldest president to assume office to date. Meanwhile, Biden’s running mate Sen. Kamala Harris (D-CA) dismissed Trump’s attacks on her “distractions,” adding: “I really think that there is so much about what comes out of Donald Trump’s mouth that is designed to be a distraction to the American people that he is doing every day.”