Center for Responsive Politics estimates that outside groups have spent at least $554 million in 2014 elections.
Del. Eni Faleomavaega (D) lost his bid, bringing the territory its first woman delegate.
Retirements and defeats will reduce the number of centrist House Democrats.
Senate Democrats have not fared much better, losing a net of at least 13 seats.
Eight races remain uncalled in California.
Former Rep. Doug Ose reclaimed a seat in Congress.
Will Hurd edged out Rep. Pete Gallego in the sprawling Texas district.
Rep. Lois Capps held on to her seat.
"Republicans earned trust of American people," said Rep. Walden.
Cresent Hardy defeated Rep. Steven Horsford (D) in an area President Obama won by 10 points.