My fundamentalist Christian family members claim:
1. That in the Bible, God put "flawed" people in power to help them see the light and test them. They truly believe that Trump is "God's Plan."
2. They also believe that he's done well for the economy. They belive I am lying to them when I indicate that Trump's numbers for the stock market (that's what they call the "economy") follow the trajectory from Obama. Mostly they just want low taxes as they turn the middle finger to those in need. See point above for the hypocrisy in this.
3. They believe that democrats are evil baby killers.
4. Lastly, they are closeted racists and like the fact that he's openly hostile to minorities. All the while they deny that he's racist because it would out them.
5. They hate 'the gays" and other 'amoral' people. They have no problems with the fact that Trump is amoral. See point number 1. They don't actually know or care about Jesus' teachings. They just do what their pastor tells them.
The gun nut people I know are convinced that Dems will take their guns. No logical counter can be made. These people are willing to sacrifice the future of the planet (that they use to hunt on) for this. Additionally, a lot of these people are blue collar folks without pensions or health care. They are literally willing to sacrifice their future and health to keep guns.
Basically, the repubs have done a masterful job cherry picking one-issue voters that are easily manipulated. They've gathered enough of them to form a "base" that has proven to be pretty much impenetrable. They rest of the GOP policies focus on helping the rich. While doing so, they convince yet more stupid people that if you vote for them, they will fix the economy so maybe one day you can be rich too.
Basically, the reason people vote for Trump is the reason they've voted for R since Reagan. This strategy has yet to bear fruit, but hey, at least they aren't commie dems that associate with Russia... oh wait, they no longer care about the Russia thing since Dear Leader says its okay.