Jeff Flake (R-AZ) has dramatically announced his decision not to seek reelection to his Senate seat in 2018:

None of this is normal. And what do we, as United States senators, have to say about it? The principles that underlie our politics, the values of our founding, are too vital to our identity and to our survival to allow them to be compromised by the requirements of politics because politics can make us silent when we should speak and silence can equal complicity. I have children and grandchildren to answer to.