I'll take this one.
You underestimate the number of moderates that exist. A lot of people do not only vote along party lines. While these people are typically lost in the conflicting political narrative in the media, if not mocked for their so-called "indecision", there are many who way candidates by character rather than policies; or polices rather than party bottom line. They exist. It is wise to never overlook them. And it would also be wise for Republicans who spit on Democrats and vice versa to take heed. There is a cost for diehard supporters becoming so impassioned by a political figure. It turns off moderates in the dozens of millions.
Republicans weren't the only ones who half assed things these last two-to-four years. Democrats share some blame for letting Trump get this far. So, Democrats took losses in the House. No follow through on the Mueller Report, their partisan politics during the impeachment cost them seats. And one shouldn't throw the Republican challengers under the bus. Perhaps they campaigned well. Certainly better than the President.
There is a strange phenomena that I observe with voters who admit to whom they vote for and it seems typical, at least where I am from, that they'll vote an oppositional President and Congressman. A try-hard libertarian tactic that if they're so focused fighting with each other and obstructing one another, then few or no laws pass. I do not subscribe to this theory but it seems to have gained more popularity in recent years and, to be fair to those who do this, it does appear to work with the current status of partisan politics in our federal government.