“If you read it, it’s pretty clear. I’m not allowed to run. It’s too bad,” Trump told reporters last October. Americans were more receptive to a president like FDR to serve a third term, given his role in shepherding the nation through the Great Depression with his New Deal. Still, people across the political spectrum accused him of endangering the country’s democracy. Although there was no restriction on how many terms a president could serve back then, the country’s first president, George Washington, had established an unwritten two-term limit by stepping down after serving for eight years. FDR’s Republican opponent,...