How can Parties and Caucuses influence voting behaviour within Congress?

-Members of Congress will often vote for their Party because they agree naturally - why else though they be a member -It can be said that 'hyper-partisanship' has made opposing political parties limit each other. For example, blocking a bill from the other party just because it's the other party -Primaries can lead to more loyalty towards Constituents and not the Party Leader - Speaker Paul Ryan, who was Republican and had a Majority in the House - had to withdraw a bill repeating Obamacare, despite the Republican's stance on it. -Congressional Caucuses also can influence voting, as the common Goal or Ideology of its members will make them vote in the same Direction