Earlier quoted context omitted.
US Senators generally are not powerful enough to have people shot.
You are assuming the violence would be carried out using senatorial powers. Senators are generally very wealthy people, and it doesn't take that much money to hire someone to kill another person[1]. 1: https://en.wikipedia.org/wiki/Contract_killing#Statistics [2] 2: I have to say I was fairly hesitant to search for that data. It's not the kind of thing you want showing up in your search history...
Far as Senators, they have bulletproof PR, low likelihood of prosecution, and ties with LEO's. They'll just ignore someone's claims, have legal action taken in a legit-looking way, or have LEO's harass the person. The latter tends to cause mental wear that makes the source's writings and actions become more erratic over time. They are dismissed as having mental illness. People are only killed when it's a straight-up blackop that they're also a serious, persistent threat to. That's rare given the selection process, planning, and field experience of those involved in such work.
So, I'd say the numbers on contract killing aren't relevant here. It's possible but unlikely. The only exception is those like Feingold deep in defense-related matters. An overlap between dirty Senators, money, and black ops has risk or results I could only guess at. I won't bother.