Here's a list of U.S. Senators telling us just how popular each is in his or her own state. The most popular — and by a wide margin — is Bernie Sanders. In Vermont, he has an 83% Approval rating versus 13% Disapproval. This is not based on a huge sample but I think it explains a lot as to why Sanders is so unafraid to advocate for positions that others might consider "unsafe."
The least popular? In Kentucky, Mitch McConnell has a 38% Approval rating and a 52% Disapproval rating. That's only slightly better than cold sores. I assume though that McConnell's problem is that he hasn't delivered on a lot of things that Republican voters feel he should have made happen.
My two Senators — Barbara Boxer and Dianne Feinstein — are both around the 50% Approval mark and around 34% Disapproval. I have no particular feeling about either because I almost never hear anything about what they're doing or how any of their votes have mattered. California currently has around 44% Democratic registration and 29% Republican and I suspect that has more to do with the two Senators' current ratings than their actual job performance.