Consider the vectors in which the rot took hold and spoke to him. Usually it’s loneliness and lack of empathy for others, triggered by a tragic event in which he couldn’t understand. A lot of the maga sway resonates with anger and frustration. Like, I hate to say it, but it’s basically just the south park “dey tuk er jerbs” reaction, but on a global scale. In other words… He may have been a rocket scientist, but he’s… Apparently not well rounded in his intelligence. No worries, though, this is normal when you’re obsessive in a career. Unfortunately, this also indicates a low likely chance of remaining cognitive placidity for getting away from the magaism. The best thing you can do is to appeal to his humanity and get him away from the constant rhetoric and to start relying on his own personal judgement again. It’s unlikely you’ll recover him more than just grouchy old man with a conservative lean, but it’s heaps better than active maga. And all that assuming you still have that influence over him or will to even try. Going off your instance, though, I’m gonna guess not.