Both can be attributed to bad candidates.
It is far more difficult to defeat a seated Congressman.
RE: We have lost one Congressional race and one Senate race.
Make that SIX CONGRESSIONAL RACES LOST — ALL HELD BY REPUBLICANS BEFORE. This does not look good for Trump’s agenda for 2018 and beyond.
See here:
https://www.cnn.com/2017/09/13/politics/special-elections-oklahoma-new-hampshire/index.html
Democrats have won 6 GOP-help congressional races. The GOP has NOT even won one Democratic seat.
If the excuse is the GOP ran lousy candidates, then every single race can be attributed to lousy candidates.