Donald Trump unleashed a handful of tweets on Saturday morning—a fairly routine practice at this point—in which he called for "equal time" from late-night hosts.
Late-night hosts like Stephen Colbert, Jimmy Kimmel, and Seth Meyers have become cultural touch points by aggressively taking on the Trump administration and congressional Republicans in their monologues. On the strength of his commentary, Colbert has surged in the ratings, overtaking Tonight Show host Jimmy Fallon—who's pulled punches compared with his peers—in overall viewers.
But the president seems to be confusing the notion of equal time with the Fairness Doctrine, which was repealed during the Reagan Administration. It required TV and radio broadcasters to present opposing viewpoints (though not necessarily with equal time). According to The Washington Post:
This meant that programs on politics were required to include opposing opinions on the topic under discussion. Broadcasters had anto determine the spectrum of views on a given issue and include those people best suited to representing those views in their programming.
The Post also notes that under the Fairness Doctrine broadcasters had to let people know if they were under personal attack in a program and give them a chance to respond. In 1987, President Reagan signed an executive order revoking the doctrine, leading to an explosion of partisan TV and radio programs.
"It’s hard to overstate the importance of the Fairness Doctrine to conservative commentators—its demise in 1987 ... is credited with the creation of modern-day talk-radio, because broadcasters no longer had to offer competing views on the same broadcasts," Politico wrote in 2011. (The rule remained on the books until 2011, when the Federal Communications Commission finally removed it.)
This is not the same as the equal time rule, which remains in effect. It requires broadcasters to give political candidates equal time. Trump's appearance on Saturday Night Live in 2015, for instance, triggered the equal time rule and NBC agreed to give his Republican opponents time on 18 affiliates during primetime, according to Variety.
UPDATE: Late Night hosts Jimmy Kimmel and Seth Meyers responded to the president via Twitter.