U.S. President Donald Trump apparently caught a rerun of “Saturday Night Live” this weekend, and decided to tweet Sunday morning that the NBC program should be investigated by the Federal Communication Commission for parodying him so much. That’s legally absurd.

But Trump’s lament reflects the persistent power of the old idea that television networks should be fair to all political sides and give equal time to all candidates for office. It’s worth asking: What’s the current state of the law on broadcaster fairness? And beyond the law, should fairness be an objective of any kind in the era of cable news and social media?

It’s important to distinguish the two legal principles derived from the federal regulation of broadcasting: the fairness doctrine and the equal-time rule.

The fairness doctrine, instituted by FCC regulation in 1949, required radio and television broadcasters to be honest, equitable and balanced in presenting matters of public importance. It applied only to licensed broadcasters using the airwaves, not to newspapers. Cable television hadn’t yet been invented.

The doctrine was challenged as a limitation on broadcasters’ freedom of speech, because it obviously affected what they could and must say. In an important 1969 decision, Red Lion v. FCC, the U.S. Supreme Court upheld the fairness rule.

The court reasoned that because bandwidth was a scarce, limited resource, owned by the government and effectively leased to licensed broadcasters, the usual First Amendment limits on regulation didn’t fully apply.

The court also hinted at a broader public right to know, albeit in language it has rarely, if ever, used since. “The people as a whole,” the court said, “retain their interest in free speech by radio and their collective right to have the medium function consistently with the ends and purposes of the First Amendment.”

Crucially, the court said, “it is the right of the viewers and listeners, not the right of the broadcasters, which is paramount.”

The fairness doctrine helped create the background expectation that television news would be fair. You’ll recognize it as the probable origin of Fox News’s now-dropped slogan “fair and balanced.”

Yet the fairness doctrine was heavily criticized, and the FCC gave it up in 1987, while Ronald Reagan was president. It was formally repealed in 2011.

That made constitutional sense. Cable news made the Supreme Court’s scarcity rationale seem hopelessly outdated, and the internet made it seem medieval.

In a world where there was no technological bandwidth limit, broadcasters seem much more like newspapers whose free speech rights can’t be limited by fairness. And treating broadcasters differently from cable channels also seems strange in a world where almost everyone has cable or access to its channels.

So the fairness doctrine that Trump wants to apply to “SNL” no longer exists.

The equal-time rule is alive, however. It’s contained in the 1934 Communications Act. It says, essentially, that if a broadcaster gives its platform over to one candidate, it must give equal time to the candidate’s competitors.

That doesn’t apply to parody, of course. Actor Alec Baldwin, who portrays Trump, isn’t running for office. There’s no other candidate being given airtime. Trump’s tweet is legally wrong.

“SNL” was actually once accused of breaking the equal-time rule in Trump’s favor — by letting him host the show in 2015. In response to the charge, NBC cut a deal with Republican primary candidates John Kasich, Mike Huckabee, James Gilmore and Lindsey Graham, giving them free airtime on affiliates in Iowa, New Hampshire and South Carolina, as well as time on “SNL” itself.

It’s tempting to conclude that Trump got the idea of equal time in his head when that happened, and has subsequently misapplied it to his parody alter ego.

Regardless of the law, should networks try to be fair and balanced on the issues or to the candidates? In the marketplace of ideas, the answer depends on what market the networks are trying to reach.

If a network genuinely wants to appear evenhanded to audiences — and advertisers — then fairness and equal time are the way to go. A clear rule should protect networks from inevitable bullying on all sides.

But there are other objectives that media can pursue beyond fairness.

For example, a network or newspaper might aim at the truth. The truth isn’t always evenhanded. Pursuing partisan balance is at odds with the truth if one side in the debate lies more than the other.

And truth itself can be divided into facts, which can be checked, and opinions, which require deeper engagement to determine the moral truth.

In their own ways, Fox News (from the right) and MSNBC (from the left) are pursuing political or moral truths that are inseparable from political viewpoint. It would be counterproductive for those cable networks to be fair and balanced.

The most we can ask is that, in the cut and thrust of public debate, opinions get challenged and analyzed, and facts get examined.

So far, government regulation hasn’t solved that problem anywhere in the world. Free speech is far from perfect. But it’s the best tool we have to produce a greater fairness, and a greater truth.

Noah Feldman is a Bloomberg Opinion columnist. He is a professor of law at Harvard University and was a clerk to U.S. Supreme Court Justice David Souter. He is the author of six books, including “Cool War: The Future of Global Competition,” and “The Three Lives of James Madison: Genius, Partisan, President.”