Roberts said in response to a Constitution Day question in the Washington Post (NYSE:WPO) about the "coolest part of the Constitution that people might not know about" that the arrangement is more than job security; it is a buffer against political pressure.

"Justices serve for life, so they can say what the law means without worrying that it might be unpopular," Roberts replied. "Because the Supreme Court is separate from the rest of the government, it can make sure the government follows the law, too."

Wednesday is Constitution Day, which marks the 221st anniversary of the signing of the document.