His support makes a little more sense when viewed through the lens of a culture war.
Link: https://www.theatlantic.com/ideas/archive/2019/07/evangelical-christians-face-deepening-crisis/593353/
...when he starts talking about St. Ambrose, and the "weaponization" of the faith.
First, the Ambrose analogy is not applicable. Does the author really fear that modern Christians won't verbally stand up to the slaughter of innocents? That's just silly.
Secondly, the faith is not being weaponized by Trump. Quite the contrary. Trump is just restoring a few secular checks and balances that were previously removed (and he still has a long way to go to get back to the center, and I don't trust that any of his changes won't be reversed by the next president).
To the author's point, though, there definitely is the perception that there is a culture war going on. One limited, particular example: It is not enough that gays be allowed to marry; Christians must be forced to endorse those marriages, or lose your right to make a living for your family. Put generally, in the words of Erick Erickson: "The Left will not let you stay on the sidelines. You will be made to care."
There is also a perception that the person fighting that culture war need not be perfect, since no one is. It is interesting that the author wants his president to be more Christlike, and therefore opposes Trump. The author has said in the past that "often Christians make the mistake of assuming the words of Christ and the individual commands, or commands that apply to individuals, apply to governments as well [but] the requirements on government is [sic] different than on individuals." (He is correct on that.) He even says, "I don’t think it’s advisable to have pacifists in the White House." (Also correct.)
Related side comment: I have a relative who adores Trump. I was actually pretty shocked by this. I mean, I support Trump as the best available option, and I will likely vote for him again, but I know his weaknesses and drawbacks, and I certainly wouldn't have him over for dinner with the family. But, she was acting as if Trump could do no wrong. I honestly think all the crazy attacks on him have given him a victim status among many, allowing them to more safely ignore the legitimate attacks (which I think is a human response, not a God-guided response). Also, Trump supporters know they will be attacked in public and even the work place if they voice support for him...so they save their comments for private political friends...such that talking about it is almost a release for them, which I suspect also leads them to getting carried away...and likely reinforces their beliefs further. Probably better to have reasoned public debate, but that is not an option these days.