Economy

On the one hand, he could dump absolutely unthinkable resources into primary campaigns. Given the sleazy tactics he employed previously, it's safe to say that any primary fight he really threw his weight into would be brutal, dirty, and incredibly damaging to everyone involved. Even if he failed to unseat the incumbent, they would have almost certainly have a diminished war chest and a lot of additional baggage weighing them down going into the general election.

On the other hand, I am not exactly holding my breath while I wait for Musk to make good on a promise. And even if he did follow through, there's no way he would just throw the money at the campaigns and let professionals handle it. He can't resist the urge to make himself the center of attention, which can only backfire.

And third, his objection to the bill is not all that shit that it does to fuck the country, it's that it isn't cutting enough. Anyone he backs in a primary is probably going to be even worse than the incumbent. The only upside there is that the even more extreme candidate might be more likely to lose in the general election. but that's not a chance I wanna take after the last election.