WASHINGTON, May 16 (Reuters) - U.S. President Donald Trump accused James Comey on Friday of calling for his assassination in a coded post on social media, rejecting the former FBI director's explanation that he was not aware of any violent connotation.U.S. law enforcement officials are investigating an Instagram photo posted by Comey of the number 8647 formed by seashells with the comment, "Cool shell formation on my beach walk."The Reuters Tariff Watch newsletter is your daily guide to the latest global trade and tariff news. Sign up here.In U.S. slang, the number 86 can be used as a verb meaning...