Andrew Jackson was president like 20 years before the civil war my guy. Ulysses S. Grant was president when the 14th Amendment was ratified in 1868. I'm not really sure how you thought otherwise. Regardless, your other point about his reference to himself as an officer is irrelevant anyways because that's not what determines him to be an officer of the court.
The actual reason is that when the 14th Amendment was being signed, the specific question of "why does it not mention president" was asked nearly verbatim. One of the writers of the Amendment, who I'm forgetting the name of, replied to them by asking them to read over the part where it says "any officer". We know this because we have the minutes from that day, we have the transcription as it was recorded by hand at the time.
A federal court already determined Trump to have engaged in insurrection. By all accounts, he should be barred from running.
There's a lot of shit to talk about the gop, that doesn't exactly mean a whole lot