system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is a 'whip' in US congress and what do they do?
gpt
The whip is a very senior role who ensures that the party leadership has the votes to pass their bills.  The job is mostly informal (the whip doesn't have a ceremonial role) with lots of behind the scenes negotiations over favors, election support money, and logrolling and other perks to ensure that the majority leader has the support of their party for their goals.  He also serves as a strategy advisor for the party with lots of information about what's legislatively possible and what isn't.  

The first seasons of House of Cards (both the UK and US versions lead character serves as the whip for their party).