The framing that congressional politicians have "forgotten" that they have power is a silly and dishonest trope. They absolutely know that they have power, but they also just watched multiple incumbents (Cornyn, Cassidy, Massie just to name a few) who didn't get Trump's endorsement lose their respective primaries, effectively ending their political careers.

Members of Congress, just like everyone else, act in their own self-interest. And unfortunately for pretty much everyone else, their best method of self-preservation is to do nothing, hence the "eunuch" Congress.