Four Democratic lawmakers have penned a letter to Biden administration officials urging them to establish vaccine requirements for domestic air travel throughout the United States. Sen. Dianne Feinstein (D-California) and Reps. Don Beyer (D-Virginia), Eric Swalwell (D-California) and Ritchie Torres (D-New York) said in their letter that people seeking to travel within the U.S. should be required to provide proof of vaccination or a recent negative COVID-19 test before being allowed to board a plane. The letter was addressed directly to Rochelle Walensky, head of the Centers for Disease Control and Prevention (CDC), and Steve Dickson, Administrator of the Federal…