The two burning issues for the bulk of evangelicals seem to be: 1) appoint enough judges to overturn Roe v. Wade, and 2) roll back legalized gay marriage. If they were to look reality in the face for an instant, the evangelicals might realize that both of these goals are pipe dreams.
Turning back Roe v. Wade — and even some of the current conservatives on the Roberts court are far from sure bets on this front — would not "end abortion." It would simply criminalize abortion, drive it underground and overwhelm the criminal justice system with thousands of cases to police and bring into the courts.
Pre-Roe v. Wade we had a high toll of annual abortions in America, by some estimates, close to one million a year, it's just that these were underground or, at worst, "back alley" abortions. That would all be revived. Besides which pharmaceutical developments now make it all too possible for women to orchestrate their own abortions, without recourse to physicians or nurses.
Gay rights and gay marriage? Trump has always been a "live and let-live type of guy" in this regard. He has not, to my knowledge, said Word One re: rolling back gay marriage. Not going to happen. (And I'm opposed to it myself, but I have no illusions about Trump trying to roll it back.}
Thus all that evangelical support for Trump may well go for nought in terms of achieving their deepest-felt objectives.
Younger evangelicals who, like many of their peers, believe in climate change and care deeply about protecting the environment, may be the first to split from Trump. They too blanche over his throwing around the g-damn word, just like their older coreligionists. They nonetheless still oppose abortion on demand.
So we may truly see some fissures in what had previously seemed a solid bloc of evangelical support.
All it would take for many evangelicals to switch to looking at a Democrat would be for Democrats to begin showing some sympathy with pro-life reasoning, e.g., let's face it, the line "women have a right to control their own bodies" does not mean "women have a right to control another human being's body, namely the emerging human being in their womb."
Or for Democrats to say, as Barack Obama himself once remarked, "Every abortion is in some sense a tragedy." A line like that would carry the Democrats far.
The bottom line, for many evangelicals, is that they see themselves engaged in spiritual warfare with secularizing — and evil —forces bent on denying the religious their hard-won place in American civic life. Rightly or wrongly, they view the Republican party, and hence Trump as that party’s leader, as a bulwark against secularism.
Republicans are more likely to be not only “flag wavers” but also those who sprinkle their political rhetoric with biblical references and hints of a Christian faith walk. Democrats speak a more secular — the evangelicals might say, a more “godless” — language. And also bow more fervently to the nostrums of political correctness that, in their extreme, consider Christian references to “sexual sin” as if that were “hate speech.”