That’s a fair number of senators! And it means that the current cycle will be the third-consecutive one with a higher than average number of senators leaving voluntarily. Roll Call has the data on members of Congress leaving office over the last forty years. In those 21 Congresses, only nine have had more than seven senators leaving by choice. Of course, it’s possible that the seven (or six, depending on how to count DeMint) who have already happened will be all, but it seems unlikely; the normal retirement season has months to go.
Oddly enough, not only are we apparently in the third consecutive Congress of a high-retirement cycle, but also this is the third time during this era that we’ve had a three-Congress high-retirement cycle. The first was in the 93rd through 95th Congresses (beginning in 1973); the second began with the 102nd Congress in 1991; and the third began in 2009. I have no idea whether it’s just luck of the draw or if there’s some causal factor at work; of course, three consecutive Senates means one fully cycle of Senate elections, for whatever that’s worth. Of the other 12 Congresses outside of those three cycles, the high point for voluntary departures was the 108th, with seven retirements and one senator (John Edwards) leaving to seek the presidency.
Since we’ve seen cycles like the present one before, I’d be very cautious about interpreting the current trend. It may just be dumb luck. None of the current retirees are young; DeMint, the youngest, was 61. The biggest trend in the Senate has nothing to do with who is leaving, anyway; it’s the advanced age of new senators. Still, I find this sort of thing interesting, and I’ll be watching to see how this cycle’s eventual totals stack up against historical precedent.