Kohser, you're purposefully picking a presidential assassin that nobody cares about (and a president nobody cares about). Oh, i'm sure someone who wanted to get it to FA and make it ten times as long could, but it would require historical books and off-internet work to do so.
Now, if you're talking about a
real presidential assassin, then fine. And he's currently at 100,639 bytes. That's a better comparison.
Furthermore, you have to add in the fact that news sources available today are much easier to access, more extensive, and go out of their way to discover minute details about a person.
Compare that to events that happened 40 or 100 years ago, and it is much more difficult to find sources on what happened that go into a lot of detail that isn't just a repetition of a standard biography.
Not to mention that those assassin's probably would have a significantly higher number of bytes, if not a whole separate article on the subject, if they had published a manifesto.