Enter the names of the U.S. Presidents who were the only living U.S. President for a period of time. (Do not include future presidents being alive, only those who had served already or currently serving).
Imagine if tomorrow, Carter, G.H.W. Bush, Clinton, G.W. Bush, and Obama died in a plane crash. The remaining living person that has been president of the U.S. would be Donald Trump. Therefore, Trump would be the only living U.S. President (current or past), until a new president was elected. Then there would be 2 living presidents, Trump and whomever was elected as the new president.