468 of the 538 seats in congress, including 100% of house seats, are up for election every 2 years. On top of this, you don't need to change every seat in cong

468 of the 538 seats in congress, including 100% of house seats, are up for election every 2 years. On top of this, you don't need to change every seat in congress, you generally only need a tiny handful to flip to switch control - for example at this moment the Senate is 51 to 49 and the house is 220 to 212 (with 3 vacancies). To flip both houses would require only 7 seats to flip, or 1.3% of congressional seats. The big difference between congressional and executive elections is that congressional changes explicitly do not represent national shifts in voter opinions as they are regional elections. Only a national election can demonstrate a true shift in voter opinions, and when such a shift occurs is exactly when laws should change.