I never put too much stock in the alleged political leanings of teenage school shooters. They are often loners searching for identities and can be Trump supporters one week and anarchists the next.
“Sickle, Hammer, and Iron Cross strike in Texas“
https://www.americanthinker.com/blog/2018/05/sickle_hammer_and_iron_cross_strike_in_texas.html
And with good reason(IMHO)
It would be amusing if it weren't so tragic, to noting that from the ring wing sources, he was "antifa" because of the "Hammer and Sickle" symbol. To the left wing, he was a Nazi because of the (misidentified) Iron Cross as "Nazi" symbol. And to the Christian wing, he was a Satanist because of the Baphomet Star and a Cthulhu symbol. He was "gay" because of the supposed "Gay Pride Heart. (He also had a Japanese flag pin but I don't think anyone pretends to knows to what this suppose to mean)
He was a "honor Student' but given the state of education today I don't know if he was smart or this just a "pat on the head"
In my opinion the guy was smart enough to assemble enough "symbols' to guarantee to piss of somebody. He was walking Teenage Angst and Rebellion, personified. A real life Rorschach test.
The real question is, why nobody saw this coming. My answer is the school was so large(1,400) he got lost in the system. Mush like other shooters from large high schools.