A Supreme Court argument on Monday about whether North Carolina may bar registered sex offenders from using Facebook, Twitter and similar services turned into a discussion of how thoroughly social media have transformed American civic discourse.

The justices’ remarks, which indicated easy familiarity with the major social media services, suggested that they would strike down the North Carolina law under the First Amendment.

Justice Elena Kagan said that President Trump, every governor and every member of Congress has a Twitter account.

“So this has become a crucially important channel of political communication,” she said. “And a person couldn’t go onto those sites and find out what these members of our government are thinking or saying or doing.”