What was the worst president assassination?

All assassinations are tragic and terrible and it is hard to say that one is worse than another. However, I would say that the Lincoln assassination was the worst because it came at an extremely difficult period in US history when exceptional leadership was badly needed. For a variety of reasons, the difference between Lincoln's leadership ability and that of his successor seems greater than that between the other assassinated presidents and their successors. Also, Lincoln was the first US President to be assassinated-- possibly his assassination made future assassinations more likely.