Tuesday night turned out to be a gentler wave than Democrats had hoped. Much larger waves have happened in American elections, the biggest being the tsunami of 1894, which washed away 127 Democratic representatives and increased Republican ranks 57%. The election of 1874 did almost the same damage to a Republican majority, drowning 100 of them and costing them 49% of their strength. The election in 1932, which brought Franklin D. Roosevelt to the presidency, also kissed goodbye to 46% of Republicans in the House.

What happened...