All it takes is Trump deciding to back an insurgent challenger to have a credible threat to even long term respected incumbents, because MAGA primary voters aren't even thinking anymore.
That's bad news for the party's long term electoral success, but it also means the incumbents aren't going to stand up to Trump or Musk.
I think there are two problems.
Republicans correctly realize that their actual MAGA base is all that's left on Twitter and Musk has the money to actually primary them or worse (and Trump's ear). And Republicans collectively haven't had spines in years to stand up to either Trump or Musk or MAGA.
a bunch of Dems are terminally online and still think Twitter is the "public square" and really haven't grasped that it is now just a Musk echo chamber. So they actually think that Musk carnival game is their constituency.