What amounts to a wave election in the U.S. House?
We define a wave as the top fifth (20%) of elections from 1918-2016 in terms of losses for the incumbent president’s party.
Under this definition, the president’s party must lose 48 seats in the U.S. House for an election to qualify as a wave. There were 11 wave elections between 1918 and 2016: four for Democrats and seven for Republicans.