I'm a bit surprised that neither of you remembered that both Rockefeller and Ford himself were simply appointed by the sitting president. Spiro Agnew was the elected vice president under Nixon, but he was also forced to reisgn for different reasons before Nixon resigned. When Nixon also resigned, Gerald Ford became the first president of the United States to have never won an election. He was appointed by Nixon and then ascended the throne. A democracy indeed. Ford then also appointed Rockefeller as his own vice president. Theoretically, every president has the ability to replace the vice president (assuming the the VP resigns or is otherwise "lawfully" removed) and then a non-elected president, like Hillary, AOC or Bill Gates, could ascend to the presidency when the elected president vacates.