Didn’t help that he showed up at his first couple Senate meetings gloating about winning the election. And tried to set working hours for his former colleagues. Among other things.
Obstructionism as a core tenet of the (former) Republican platform is reprehensible, and retrospectively probably led to quite a bit of discontent with the government’s inability to address problems that Americans face. That same discontent fomented the current reactionary swing, so in the end maybe they really got what they wanted. Shameful.