If they can’t control him then they’ve already functionally lost a seat (unless of course, they actually like having him block legislation they don’t actually want to pass)
Parties exert control on their members in this country, they always have, and generally not through violence or torture. Usually its through taking away party support from them and their personal agenda. It could be attacking political pork to West Virginia, close military or other government facilities there, and support challengers/kick him out of the party so he can’t run on their ticket. It could possibly include more strong-arm tactics, not violence, not even anything necessarily illegal, that’s speculative but possible.
What you’re asking people to explain, is something that is the norm. You’re the one actually making an outrageous claim of how do we expect a political party to control and discipline its members. And pretending that the Democratic Party or the President just have no power in this situation is ludicrous