carry someone's water
to occupy a subservient position, to do the bidding, the menial tasks, and frequently the dirty work, of a more powerful person, and is most often used in a political context.
subservient
prepared to obey others unquestioningly.
menial
(of work) not requiring much skill and lacking prestige.
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roll over
If you say that someone rolls over, you mean that they stop resisting someone and do what the other person wants them to do.
