Politics Joe Biden Laughs Off Trump's Attempt to Paint Him as Senile: 'Watch Me, Mr. President. 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," Joe Biden said of his and running mate Kamala Harris' health By Benjamin VanHoose Published on August 23, 2020 03:45 PM Share Tweet Pin Email Former Vice President Joe Biden (left) and President Donald Trump. Joe Biden plans to demonstrate his cognitive stamina to dispel Donald Trump's attacks. In a clip from a new ABC News interview, airing Sunday at 8 p.m. ET, the 77-year-old former vice president laughed off the claims from the Trump campaign that paint him as senile and "diminished." Biden told World News Tonight anchor David Muir that it's a legitimate question that he will prove wrong by his actions. "Watch me. Mr. President. Watch me," Biden said, adding of himself and his running mate Kamala Harris: "Look at us both. Look at us both, what we say, what we do, what we control, what we know, what kind of shape we're in." "I think it's a legitimate question to ask anybody over 70 years old whether or not they're fit and whether they're ready. But I just — only thing I can say to the American people, it's a legitimate question to ask anybody. Watch me," the Democratic presidential nominee said. If elected, Biden would be the oldest president to enter the White House, as he turns 78 on Nov. 20. In the interview, Biden also said he is open to running for a second term if he wins the upcoming presidential election against Trump. Biden has been repeatedly attacked by Trump, 74, for his reduced public appearances during the coronavirus pandemic, with the president nicknaming his 2020 opponent "Sleepy Joe." Biden laughed off a question about "cognitive decline" earlier this summer, assuring that he's "constantly tested." 13-Year-Old Boy Who Stutters Makes Touching Speech About How Joe Biden Made Him Feel Confident “I’ve been tested and I’m constantly tested,” he said at the time. “Look, all you got to do is watch me. I can hardly wait to compare my cognitive capability to the cognitive capability of the man I’m running against.” Last week, Biden and Harris, 55, gave their first joint interview as running mates to PEOPLE, as Biden explained why he chose Harris as his vice-presidential candidate. “It’s really, really, really important to have someone [like Harris on the ticket] with this intellectual capacity, educational background, backbone and stature,” he said. “It's going to change a lot.” Harris — who became the first Black woman and first person of Asian descent to join a major party’s presidential ticket — applauded Biden for vowing to select a woman to join him on the ticket. RELATED VIDEO: Joe Biden & Kamala Harris' First Joint Interview: 'Audacity' of Partnering and Their 'Modern Family' Values Behind the Scenes of the Zoom Call That Changed Kamala Harris’ Life: When Biden Asked Her to Be VP "Joe Biden had the audacity to say he was going to have a woman as his vice president. He didn’t apologize for it. In a country where we still have so much to do to fight toward our ideals, he just fast-forwarded the whole thing," she said. "The government should look like the country," Biden said. "There's a new law of physics in politics: Any country that does not engage more than half their population in sharing the full responsibilities of governance and power is absolutely going to lose." The Ticket: The First Interview, a special edition of 20/20, airs Sunday at 8 p.m. ET on ABC.