Pollsters estimate that Republicans still have >30% chance of retaining the Senate majority. (Better than what pollsters gave Trump before he won in 2016.)
This isn't a deeply unpopular anomaly. This is a significant chunk of America, and they may easily regain the majority if the economy improves in a few years (or if it worsens further under a Democratic president).
This isn't a deeply unpopular anomaly. This is a significant chunk of America, and they may easily regain the majority if the economy improves in a few years (or if it worsens further under a Democratic president).