evidence: U.S. President Joe Biden was a "full professor" at the University of Pennsylvania for four years. [...] In mid-to-late 2023, a number of posts on X and TikTok circulated showing U.S. President Joe Biden saying he taught "political theory" at the University of Pennsylvania (UPenn) for four years. The posts argued that Biden was lying, and that he "never taught a single class at UPenn." Questions about Biden's role at UPenn have circulated for years. In mid-April 2022, for instance, his critics latched on to a speech in which he claimed to have been a "full professor" for four years at the university.