As of July 11, 2020, there have officially been 45 U.S. presidents. Theories abound regarding the power held by figures such as Dick Cheney or Edith Wilson, but the official tally stands. Should it?

The presidential line of succession is an important mechanism to ensure that, at any point in time, someone occupies the office. In 1849, the president pro tempore was third in that line of succession following the president and vice president. The president pro tempore at that time was David Atchison, Democratic Senator from Missouri. Before the Twentieth Amendment to the Constitution, presidential terms began on March 4th. The incoming president, Zachary Taylor, was to be inaugurated on a Sunday, but Taylor’s religious beliefs compelled him to delay the inauguration by one day.

This created a conundrum, as the outgoing president, James K. Polk, would no longer be in office on that Sunday, nor would his vice president. This meant that the line of succession fell upon the president pro tempore, David Atchison.

Had Atchison taken the oath of office, that would have legally made him President of the United States, correct? That is where the claim becomes trickier, as Atchison’s Senate term had expired the day before and a new president pro tempore had not been sworn in. Despite this, David Atchison continued to claim until his death that he had been the U.S. President for one day, and that it had been “the honestest administration this country ever had.” Even his epitaph pronounces that he was “President of the United States for One Day.”

In all likelihood, given that Atchison’s term had already expired, and a new president pro tempore had not been inaugurated, there was no president on March 4, 1849. It is, however, tough to argue that this power vacuum wasn’t the “honestest” administration possible, so at least an element of Atchison’s claim holds water.