Passage: Under the Twelfth Amendment, the Senate has the power to elect the vice president if no vice presidential candidate receives a majority of votes in the Electoral College. The Twelfth Amendment requires the Senate to choose from the two candidates with the highest numbers of electoral votes. Electoral College deadlocks are rare. The Senate has only broken a deadlock once; in 1837, it elected Richard Mentor Johnson. The House elects the president if the Electoral College deadlocks on that choice.

Question: when was the only time that the Senate broke a deadlock?
1837