Can anyone find this story for me? It's one of those early sci-fi short stories. A dictator is violently deposed but escapes by jumping into a time machine. He travels to the past (somewhere around the present) and ends up staying with a couple in (sounds like) Appalachia, but everything on their farm starts withering and pretty soon they die. As he moves on it becomes clear that everything that's exposed to him for very long dies.
It turns out he is radioactive, because he's from the future, and everything's nuclear there and humanity has adapted to it (don't ask how!), so his body contains so much that it's lethal to people in our era.
So, if I remember correctly, he is not only hunted down and killed but a massive concrete bunker is built over his body to contain the radioactivity, which later turns out to be the foundation of his palace in the future. Or else he escapes. I can't remember!