US Senator. Twice elected as a Senator from Missouri to the United States Senate, serving first from 1843 to 1848, then from 1849 to 1855. Served as President Pro Tempore of the Senate in 1849. The term of President James K Polk ended on Sunday March 4 1849, and President-Elect Zachary Taylor refused to take the oath of office on a Sunday, so Senator Atchison is said to have been President of The United States for one day. In reality President Polk's term was extended for one day, and David Atchison spent the entire day he was supposed to have been President in bed. Atchison Counties in Missouri and Kansas are named for him.