Corker has been reelected only once, in 2012. He did not face a serious (or even half-serious) primary challenger so there was zero chance he would not be returned.
He’s up again in 2018.
Yes, and he will probably keep getting reelected. Sadly, that's how it works here most of the time. TN is a Republican state and some people think all Republicans are good. I hope and pray people are watching what is going on and decide to give him the boot but I don't expect it. We need a good conservative that is well known to run against him instead of a good conservative that nobody has ever heard of.