The power to conduct border searches, even without probable cause, is considered well-settled under the law as not contravening the Constitution. See, e.g., U.S. v. Ramsey, 431 U.S. 606 (1977).

From the case's dissent: "If the Government is allowed to exercise he power it claims, the door will be open to the wholesale, secret examination of all incoming international letter mail. No notice would be necessary either before or after the search."

Viewed from a post-Snowden perspective, it sounds predictive.

Segregation, too, was once considered well-settled. That didn't make it right nor consistent with the Constitution, which has not changed its language on the subject since 1868.