What does a new Democrat-dominated party system look like?

[Non Swing Voter]

there is a lot of lasting damage the current GOP has done that will take years to correct (the courts, the environment, gun control, civil rights, etc.) so I think it will last longer than people think.  The GOP is also too hard headed to change their ways.  Look at the idiots they keep running in Virginia knowing they aren't electable.  So the coalition would be exactly what it looks like now and Democrats will probably dominate politics for a while, with Republicans occasionally winning the senate.  But they probably won't put garbage politicians like Mitch McConnell in charge.

[Non Swing Voter]

This is kind of building up/actually happening.  The problem for them was that the rustbelt flipped before the sunbelt did.  But I think they could maintain this coalition for a few cycles before new divisions in the electorate occur.  They could have a huge margin in the house with a lot of seats on the two coasts + Illinois.  Plus a small margin in the senate.  It would probably happen all at once. Basically like what happened in Virginia.  They could have a sustainable majority based on just urban/suburban states and districts the way Democrats do in Virginia without any real rural support at all.  Which means they could just push through their agenda (especially on social issues) without fracture.