You can say tricked them into believing something (their power etc.) and then at a critical moment pulled the rug from under them/left them high and dry. Hope this helps, Hunter! :)

Great examples Philip…. To leave someone high and dry……was the only one that came to my mind.

I don't think English has a direct idiom for that, but these are similar, though probably only used by older people: "Now the shoe is on the other foot." and "How the tables have turned." both mean that our situations have inverted. To "pull the rug out from under someone" means to withdraw your support. To "leave someone high and dry" means to refuse to help someone.