evidence: President Joe Biden served as a professor of practice at the University of Pennsylvania starting in 2017. His duties went on for about two years instead of four because he went on unpaid leave in 2019 to run for president. [...] "Our democracy is under attack, and we got to fight for it," Biden said. "I taught at the University of Pennsylvania for four years, and I used to teach political theory. And, folks, you always hear every generation has to fight for democracy." Is Biden right about teaching for four years at the University of Pennsylvania?