Three tings to know, from an useful discussion on Hacker News:
1. $1M is a pretty small price to pay to have a 50/50 shot at CTO of the USA.
2. I'm sure he'll see a very significant ROI on his $1M once the government starts awarding contracts very conveniently to companies of which he owns a portion.
3. Trump doesn't really 'owe' Thiel anything, because Thiel doesn't have direct future influence etc., and Trump doesn't need him in the future.