History and current trends suggest Republicans will likely pay a political price for controlling the White House, but how big a price is unclear.
In the House, Democrats need to flip 24 seats to gain control – currently a 50-50 proposition. Democrats benefit from President Trump’s poor approval; Republicans benefit from incumbency and a GOP-leaning map.
In the Senate, 25 of 33 seats up are held by Democrats (or Democratic-leaning independents). At least six Democrats are vulnerable. Republicans have eight seats to defend; few are competitive. Republicans will likely hold the Senate unless there’s an anti-Trump wave.
– Larry Sabato, Sabato’s Crystal Ball, University of Virginia Center for Politics