So, as a rough, the board determines what happens, and the shareholders can notionally replace the board. The board _can_ listen to the shareholders, but are by no means obligated to and in the case of Twitter in particular, the board elections happen on a staggered rotating basis so even a majority shareholder could not immediately replace enough of the board to obtain a majority.
This is totally false. The board owes a fiduciary duty to shareholders. It is almost certain that if they imploded the deal for political reasons that places like florida would have sued.
The fiduciary duty exceeds expressed shareholder preferences -- if the board believes that a particular action is not likely to improve value, they don't have to do it, even if all their shareholders tell them to (though, of course, they might be likely to be voted out in the next election for same).