And if that's happening, we should nail them. If Trump can prove that members of Congress, or officials from the White House, told Twitter (or any other company) - "do what we tell you or we'll **** you up" (or any other sort of threat), that's a serious breach and something we should raise hell about.
But I don't think that's established. It's certainly possible. But it seems to me more likely that these companies are simply sick of Trump's trolling. They're also facing very real and intractable problems with people using their platforms to spread propaganda, and their at a loss for how to deal with them, legally and practically.