Question: what is the job of the whip in congress?
Answer: to ensure party discipline

In countries influenced by the British political system, a whip is an official of a political party whose task is to ensure party discipline in a legislature.  Whips are the party's "enforcers"; they invite their fellow legislators to attend voting sessions and to vote according to the official party policy. The term is taken from the "whipper-in" during a hunt, who tries to prevent the hounds from wandering away from the pack.