Everyone is applauding this because they hate Trump, but take a step back and see the bigger picture. This could backfire in serious ways, and it plays to Trump's base's narrative that the mainstream media and tech giants are colluding to silence conservatives (and maybe there could even be some truth to that.) I know the Valley is an echo chamber, so obviously no one is going to ever realize this.
It can’t be all perfectly achieved, but to do nothing, as they were before, could be now determined to be a worse case than providing these annotations to flagrant misuse by the highest impact profile that they can’t do away with entirely.
It's within their rights to do take these actions, fact checks and hiding/deleting tweets, to protect their ecosystem. If it is questionably legal because it may influence the election, then I haven't seen the law it is breaking. I see a better argument for showing Twitter promoting Trump's feed to drive clicks as an in kind donation which could quickly break legal campaign donation limits.
Twitter has taken a stand here and I do think they should apply their policies evenly. Will they effectively apply this to everything or even have the capacity built out now to do so? I doubt it. They are a business who needs user engagement to drive profit from ads. If they constrain their most clicked tweets it could lower their revenue even if initially those tweets get attention for being removed.