Politico: If Dems lose, blame Harkin, Johnson, Baucus, Levin, and Rockefeller

[Mister Mets]

They should have retired in 2008.

There's a strong argument.

Politicians have a tendency to stick around during what look like good cycles, and to leave before bad cycles. It's a bit like the snake eating its own tail. The fear of being in the minority leads to popular incumbents quitting which increases the chances they'll be in the minority.

That said, some incumbents are in trouble as well. If Rockefeller had left in '08, there's no indication that the Democratic candidate would be as strong.

[Mister Mets]

Between 2006 and 2012, Republicans defeated a total of two Democratic incumbent Senators (Feingold of Wisconsin, and Lincoln of Arkansas.)

They unseated five in 2014 (North Carolina, Louisiana, Arkansas, Colorado, Alaska.)

This was not an election in which incumbency meant all that much.