Maybe I could have said the Republicans have retreated into their own camp rather than isolated in a bubble? They have circled the wagons as they see their cherished vision of America under assault from Liberal Tribes.
That said, surely you agree the Democrats are a much more inclusive party? Indeed, in 1968 they were a mosaic of special interests who could not prioritize one over the other though they tried, with the result the 1968 Convention was chaotic and with Vietnam in full swing and LBJ walking off stage, they lost, and again in 1972.
It may be that the demographic changes since then have advantaged the Democrats but I think you will agree it is often the case that immigrants are economic and also often social conservatives, which makes a mockery of the silly claim Trump and others make that immigrants are encouraged by Democrats to cross the border as they then vote Democrat and replace 'indigenous' Americans because they have 10 children, and so on.
I believe immigrants want to prove they can make it in America without hand-outs, I think this/has been important for Korean and other Asian immigrants.
Also, while I think most Americans vote not on party lines but on the basis of their interests, there are still tribal affiliations, as with the 'Evangelical Christians', the White Racists, the 'Black Vote' which may not be as secure as once it was, but cannot be denied as a crucial vote for the Democrats in the South. After all there once were 'Reagan Democrats' and the multitudes who voted for Obama who were not normally Democrat voters. And so on.
The real puzzle in America, is that the Right to Vote might be enshrined in Law, but each State can interpret that law in its own way, so while it might claim not to deprive people of the Right to vote, the conditions attached in effect mean the vote being taken away -convicted felons who cannot vote, or not vote if released from prison but not having paid a fine, for example. Registration issues, voter ID issues, polling stations in majority Black areas closed on polling say for 'Health and Safety' reasons -sometimes in the US it is not party affiliation or class or religion that matters, but the simple fact that if the Republicans fear for their majority they will use 'State's Rights' to rig the election in their favour.
You might say, in such an election, the voters have been trumped. 2024 is going to be, shall we say, interesting...