How many seats the GOP needs to lose for a "blue wave"

How they got the numbers

Ballotpedia defines a "wave" election as "one in which the net seat change by the president's party falls into the top quintile of historical changes." They compiled data from 1918 to 2016.

• U.S. House: In 11 of the 50 elections since 1918, the president's party lost 48 or more seats in the House. Six of those 11 "wave" elections occurred during the president's first midterm election.
• U.S. Senate: In 10 of the 48 Senate elections since 1918 the president's party lost seven or more seats. Three of those 10 "wave" elections were in the president's first midterm.

Down-ballot: Republicans would need to lose seven gubernatorial seats, and 494 state legislative seats for those to be considered "wave" elections.

Bottom line: Democrats need to pick up two dozen seats in the House and claim a net gain of two seats in the U.S. Senate to win both of those chambers. Even if it's not considered a "wave," that'll be a win for the Democratic Party.