Story highlights Most senators have resigned to fill other government posts

Two in three resignations happened before the end of the Civil War

Only four senators besides Franken have resigned due to scandal over the last century

Washington (CNN) Al Franken will become the 323rd member of the Senate to resign from office in the coming weeks. But what do we know about the 322 who came before him?

Resignations amid scandals are rare: Before Franken, only four Senators had called it quits in the midst of a scandal in the last century, according to a list of resignations from the Senate Historical Office

Franken, D-Minnesota, announced on Thursday that he'd leave his post in the coming weeks after being accused of inappropriately touching multiple women before and after he was a senator. More than two dozen Democratic senators called for his resignation Wednesday, and an Ethics Committee investigation was already underway.

But a majority of the resignations since the country was founded have happened because the senator was moving to another government post. Here's a full breakdown with data from the Senate Historical Office:

Nearly a quarter of the resignations (23%) have happened for some kind of executive branch appointment, while about a seventh (14%) quit to run for governor or another state or local office. About one in ten (11%) quit to join a federal or state or local judiciary and 7% quit for a diplomatic appointment. The number of those moving to an executive branch post has climbed dramatically, from 15% before 1850 to 34% since 1850.

Read More