Of the 44 men who have so far served as President of the United States, Historians generally agree that the term of William Henry Harrison, which lasted from March 4, 1841 to his death on April 4, 1841, was the shortest.  “But wait!” says the trivia collector at the end of the bar, ready to take bets from all patrons, because he knows that’s wrong.   “I can name a president who held the job less than that!”   “No!” respond the other customers, sure that the old souse doesn’t know what he’s talking about.  But he does—sort of.   So when the bar patrons place their bets, the old souse offers up a name, and the arguing begins. The name, of course, is David Rice Atchison, a Democratic senator from Missouri, and the storied “president for a day.”  Your school textbooks and restaurant placemats with the portraits of all the presidents might never have mentioned him, but he was real, and quite popular in his day.  He was popular enough in the Senate for his c...