President Barack Obama, right, and President Donald Trump, left, arrive at the latter's inauguration on January 20, 2017. J. Scott Applewhite/Pool/AP/Anadolu Agency/Getty Images Trump reportedly asked Obama to reveal his biggest mistake, according to a new book. In January 2017, Trump and Obama rode in a car together on the way to the presidential inauguration. Obama reportedly paused and looked at Trump before saying that he couldn't recall such a mistake. See more stories on Insider's business page. For years, former Presidents Barack Obama and Donald Trump have been political adversaries, which was never more evident than during the 2016 presidential election.Obama felt that former Secretary of State Hillary Clinton, the Democratic presidential nominee that year, was supremely qualified to be commander-in-chief thanks to a career in public service as a US Senator from New York as well as her work as the top US diplomat.However, after Clinton lost the presidential election to Trump, Obama had to start planning for what was next.On January 20, 2017, as Trump was set to be inaugurated as the 45th US president, Obama rode in a presidential limousine with him and Republican Sen.