Slight caveat to this: stations are required to run ads from political candidates, not third party organizations like PACs. Those aren’t considered political speech, and over-the-air broadcasters can make whatever editorial decisions they wish regarding them. That’s why any ads that aren’t paid for by a specific candidate’s campaign have to say that they’re paid for by “the Democratic Party” or “Keeping Freedom Free Coalition” or “Friends of Dan Dipshit” or something.