The EO was not the only factor. He was included in the Presidential visit to early post war Germany, and presumably clocked some of the high tech (Schauberger, etc Glocke etc) which maybe explained the observed 'foo fighters' of WWII. Whatever, he had a great interest in 'ufo' stuff, and reportedly included some in pillow talk with Monroe and was getting assertive  with wanting to know the real details. IIRC that was a final straw. The trail leads to paths which need snowshoes and a liking for some strange stuff.