We all know the order of American Presidents, right?  Washington, Adams, Jefferson, Madison, Monroe, J.Q. Adams, Jackson, Van Buren, Harrison, Tyler, Polk, Atchison, Taylor, Fillmore... wait a minute... Atchison?

On March 4, 1849, a truly unusual piece of American presidential trivia unfolded, one that to this day causes dispute in the eyes of some historians.  A devoutly religious man, President-elect Zachary Taylor refused to be sworn in on that date as it was a Sunday.  Vice President-elect Millard Fillmore also would wait until the following day, perhaps because if Taylor wasn't going to show up no one else would either.  So, as the term of President James Knox Polk expired, he readily turned over the reins of American presidential power to...?  Well, no one in reality, but some claim that David Rice Athicson (pictured at right) served as de facto Acting President that day.

Atchison, who in 1844 had been elected to the Senate from Missouri, had served as President pro tempore of the Senate during the 30th Congress.  Under the Presidential Succession Act of 1792, Atchison was next in the presidential line of succession - after the Vice President - so by that logic he was Acting President, right?  Eh... not exactly.

Under the rules of the Senate in effect at the time, it elected a President pro tempore to serve until it adjourned.  Rather than being a "continuous" office as it is today, when a Senate was out of session, the President pro tempore was technically a vacant job.  So, on March 3, 1849, the 30th Congress adjourned at which point Atchison's service technically ended.  It wouldn't be until the 31st Congress convened on the afternoon of March 5th when the Senate would elect a President pro tempore - Atchison - by which time, Taylor and Fillmore had been sworn in.

So while the tombstone of David Rice Atchison reads "President of the United States for One Day - March 4, 1849," in fact for a period of roughly 24 hours the United States went without both a President and Vice President.