That's a piece of it for sure, but just as a surface level example.

It's not just that the bible is used justify slavery. It's that the support of slavery is entirely consistent with biblical teaching.

Christianity has been, and currently is, used to propagate all kinds of awful shit. Problem is, Christianity as a whole- as well as pretty much every other major religion- relies heavily on logical fallacies, magical thinking, and faith.

Religion is already shaky footing, and it gets worse once we apply science and critical thinking.

You have to disregard facts in favor of faith and dismiss critical thinking in favor of compliance, in order to accept most of this to begin with.

Most Christians can now accept that slavery is immoral, but that's because our collective moral compass has improved, not because it's in conflict with their holy book.

And those Christians who use the bible to justify slavery, while unarguably immoral, are entirely consistent with the book. Those who don't use the the bible to justify slavery, have simply compartmentalized an element of the book that is absolutely at odds with their own moral compass.

My point is, in terms of Trump, the same sort indoctrination that makes people willing to ignore objective facts, sound science, and even their own moral compass, in order to justify this vague "spiritual" thing in their heart that they just know that they know that they know, is the same indoctrination that allows them to ignore all the obvious signs that Trump is simply using them as a means to occupy the office of the presidency, and doesn't at all give half a fuck about them or their god.