in citizens united the court built on a previous ruling that money = speech in the context of political contributions, so congress (or the states) couldnt regulate citizens' political speech by telling them what amounts they could contribute to their favored political candidate. in the same way that congress cant pass a law that says G2 cant stand outside and tell everyone how much he loves president trump. not that it would ever need to pass such a law.
i dislike citizens united very much, but i dont think this ruling has anything to do with it. but as usual, i could be wrong.
this is a major questions doctrine/ieepa/taxing power/statutory interpretation question. the early commentary is interesting in that it talks about the roberts court's take on restricting congress' ability to delegate its powers to the executive, which would be a wonderful thing if congress would actually go back to doing its job.
sarah isgur has a comment on it in the times from back in december that people are pointing to as prescient, if youre interested.