Overrated
-The age-gap. For one, Trump cut significantly into it in 2016, and the Senate races had even smaller ones (or none). Secondly, while there are more conservative and more liberal age cohorts, all do get somewhat more Republican as they age.
Underrated
-The absolute Democratic collapse with Christians (both evangelicals and Catholics), largely due to family values and abortion. If the Republicans can extend this to religious Hispanics and blacks, the Democrats will have to become socially conservative or be irrelevant for good.
He hasn't cut into it significantly enough to change the fact that the Millenials are still an overwhelmingly Democratic voting generation. Also, that "people get more conservative as they age" myth is bunk, multiple studies have demonstrated that the vast majority of people maintain the political identity they developed in their early adulthood. Granted, this is prone to more change during realignments, but the overwhelming consensus is that Democrats will be the ones reaping the windfall of the next realignment as the Reagan coalition collapses.
Evangelicals have been an overwhelmingly Republican voting bloc for the past three decades, and their political influence is past its peak. White Catholics, while still a Republican leaning bloc, have by no means abandoned the Democratic Party. White Democratic Catholics aren't at all a rarity, but what has been a far more noteworthy demographic trend regarding White Catholics is actually how quickly their affiliation numbers have atrophied due to religious switching, mostly to unaffiliated. It's also worth noting that the largest swings towards Trump among White Christians in the past election were among Christians who were the
least religious, i.e., possessed low levels of religiosity (low church attendance, infrequent prayer, little involvement with religious groups and activities, etc.) I don't think they are all of the sudden attracted to the family values shtick, if anything Trump was likely successful specifically because he was such an inadequate proponent for traditional conservative Christian orthodoxy.
Republicans have done nothing to make inroads with minorities and Donald Trump is doubling down on the most alienating rhetoric possible. Blacks and Hispanics continue to vote overwhelmingly Democratic, no small thanks to the fact that the Republicans pretend that prominent issues facing their communities don't exist. Until the Republicans change their approach with how they engage with these communities, no amount of preaching for social conservatism is going to bring more of them on board.
Which it shouldn't, because social conservatism is at its absolute nadir and its not rebounding anytime soon. I know you've cited studies regarding Generation Z being more churched than Millenails, but cherry picking a couple of data points that fit your preconceived biases does not a trend make. The studies conducted regarding social identification of Generation Z are wildly variable in their conclusions, indicating them simultaneously being the most conservative, most liberal, most churched, and most unchurched generation. This is likely in no small part due to the fact that the vast majority of Generation Z isn't out of high school yet, and thus haven't had time to formulate their own demographic and identity signals independent of their family background yet. We're probably around 5-10 years away from a reliable dataset regarding what generation Z actually thinks regarding politics and religion.
