evidence: "The rule is the Prez, and the Veep never travel together, for obvious reasons," said the March 20, 2021, post. "Then why the hell is this happening? More importantly, why is no one saying anything about it??" [...] Officials say there's no formal rule about the president and vice president riding together on Air Force One, but there's a longstanding practice of avoiding that for security reasons. [...] They travel separately due to the risk of terrorist attacks or other natural accidents, said John Fortier, executive director of the Continuity of Government Commission at the American Enterprise Institute, who has done research on the U.S. presidency.