How many senators have resigned their seat?

In the abstract, there’s nothing particularly weird about Sen. Al Franken (D-Minn.) announcing that he plans to resign his seat. It’s not something that most senators do, certainly, but it’s not unheard of. More than 300 senators have resigned at some point in U.S. history, several more than once. Often it’s because they’ve gotten new jobs — as in the case of Attorney General Jeff Sessions, who resigned earlier this year — and occasionally, as in Franken’s case, it’s because of scandal or rumors thereof. But it happens.

It’s just that if you had to look at the two senators from Minnesota and the histories of their seats and guess which of the two would end up having something weird happen, you’d have picked Franken.

It used to be that resignations from the Senate were much more common. Before the Civil War, there were an average of 2.7 resignations a year from the Senate. From 1866 onward, the average was less than one. You can see that drop-off if we look at resignations in five-year chunks since 1790.