March 29, 1905
Prior to the introduction of the American League onto the sporting public in 1901, there was a National League franchise in Washington that from 1891-1899 went by the nickname “Senators.” Before settling on Senators, the team went by “Statesmen” and “Nationals” in previous incarnations, but neither of those names stuck longer than a few years. By the time the National League Washington Senators disappeared in 1899, the name “Washington Senators” was established as the name for the baseball team in the D.C. area.
When the Washington American League club was established, they were essentially without an official nickname. Newspapers didn’t really go for the name “Washington American League club” so, out of habit perhaps, they were stuck with the label “Senators.”
In 1905, the team’s owner Thomas C. Noyes made an effort to distance his team from the National League version of the Senators by allowing a committee of writers to vote for a new nickname. On March 29, 1905, just prior to the start of the team’s fifth season, the writers voted to call the team “Washington Nationals.”
For 50 years, the club’s official nickname was “Nationals.” They were rarely called that, however, in large part because the very writers who voted for the new nickname had such trouble applying it the actual team. Through the years the references to the Senators in the newspapers outnumbered the references to the official nickname. Finally, in 1955, Calvin Griffith made the name official, changing the team from the “Nationals” to the “Senators.”
For more on the history and a little of my personal venting, here is my original post on the matter.