Chief Justice John Roberts of the U.S. Supreme Court has expressed concern about a developing situation in the United States, where people are growing up without understanding the government’s role or the workings of the legal system, describing it as a significant issue during a talk at Georgetown Law on Monday.

Without identifying specific individuals, the 70-year-old appointee by George W. Bush advised “young people” and the general public to refrain from criticizing the justices, in response to recent critiques and calls for impeachment from figures like President Donald Trump and others in recent months.

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“It’s a good thing, and I’m sincere. It is a good thing,” Roberts said, when asked how he handles public criticism. “I mean, the court has obviously made mistakes throughout its history and those should be criticized,” he replied. “So long as it is in terms of the decision, really, and not ad hominem against the justices.”

On Monday, Roberts said that when it comes to strengthening the rule of law, “one area where it’s most endangered” is with the younger generation. He noted how there is less emphasis on civics classes in schools these days and said it’s alarming “how many people have really no understanding of what the role of courts are, what the different branches have to do, really even the notion of what law is and what a constitution is.”

One suggestion Roberts had was educating people at a young age.

“You have to start as early as you possibly can, because otherwise it doesn’t become part of their understanding of government,” Roberts said. “We’re developing a situation where a whole group of young people is growing up having no real sense about how our system of justice works.”

Asked how he is able to maintain a collegial work environment with the other justices and make rulings on critical issues pertaining to the president and government, Roberts told the Georgetown crowd: “We have to work together on these things that are difficult. You find a way to get along … If you’re sort of really at each other’s throats with bad feelings and stuff like that, it just — it’s not a good way to function.”

In March, Roberts issued a rare public statement condemning those publicly calling for judges to be impeached over disagreements with their rulings.