There had to be a balance in editorial content
This rule was was the Fairness Doctrine, and it was in effect from 1949 to 1987. So it's fair to say that Reagan got rid of it.
if the station supported Candidate A, Candidate B had to be allowed equal time.
This is a different rule called the Equal Time Rule, and it's still in effect today.
Recently this rule was in the news when Stephen Colbert interviewed Senate candidate James Talarico on his (now concluded) show, without offering the same interview time to Talarico's primary opponent Jasmine Crockett. I believe in the end the interview was cut from the over-the-air broadcast to comply with the rule. (The interview segment was published on YouTube, which is not subject to the rule.)

