The Democrats have always had extremes as well as the Republicans. The extremes of both parties has grown because of countering arguments.
The Speaker of the House working with the Party's leaders have always been able to keep control. Now, Congress has turned into a "magic mike" event with the controlling party being the only one that has a say. No leadership in either party to unite.
I would say that at least 20% from each party is affecting the 60% in the middle. OAC-MTG, Gatze - Walters, Jordan -Shift, and the list goes on and on.
It is a 360 degree vicious cycle of which is totally dependent of who is in charge. Trump grew the division which is ok, but did it with the wrong intent and did so without the consciences of the Party.
The Republicans will possibly suffer because of issues like abortion and others not Trump's fault but a Red Meat issue that has label the Republican Party. If the Republican Party loses the Presidential Election and both Chambers it will be because of the shift in the Independent voter. Commonly referred to as a "Moderate" which the Republican needs to win. All the Democrats have to do is put a viable candidate up to appeal to this group and not an incompetent, braindead individual. Neither Projected Candidate really appeals to the true Moderate voter so when given a choice they don't vote or hold their nose and vote or vote based on issues.
.