President Trump on Friday renewed his attacks on the former F.B.I. director James B. Comey, kicking off a morning Twitter barrage by once again accusing Mr. Comey of leaking classified information and lying to cover it up, even as the leaders of North and South Korea held a historic meeting hours earlier.

In a tweet, Mr. Trump called Mr. Comey “either very sick or very dumb,” saying his fired F.B.I. chief did not understand the severity of his actions in having details about his interactions with the president provided to a reporter. “Remember sailor!” Mr. Trump added, a month after he pardoned a United States sailor who had pleaded guilty to illegally retaining national defense information and obstruction of justice.

The sailor had taken cellphone photos in restricted areas on a nuclear submarine and destroyed them when he learned he was under investigation.