I'm not from the U.S. and therefore not Republican or Dem and I certainly don't have anything groundbreaking information to add to the debate but I do think that one of your assertions is a bit silly.
You say - "I don't know how someone who couldn't manage a simple functional bomb could manage a graphics program to custom print that absurd collage of cartoonish over the top Alt right flavored nonsense." I know loads of people capable of putting together a shitty collage like that together including my pre teen kids with no problem at all. I consider myself a graphic design luddite by even I could manage that but I (or anyone else I know) wouldn't have the first clue about putting together an explosive of any sort. The other thing is that you can safely practice photoshop, word or whatever and make as many mistakes as you like without blowing yourself up whereas going through the other process and making mistakes could end up in a case of extreme mutilation! Maybe the guy was scared of doing just that and couldn't follow through.
I don't know I just wanted to make the point that daft assertions and statements just lessen the impact of your article - just saying....