Why might a Congress member vote against his or her personal beliefs?

From Wikipedia:

In the US Congress, it is the function of the party whip of each party in each house has the function to ensure that members adhere to party policies and in particular that members vote for or against bills, amendments, and (in the case of the US Senate) for or against treaties and administration appointments as determined by the senior party leaders. The leverage available to the party whip may be in rewards (such as the negotiation of side deals for pork-barrel spending) or in punishments (such as withholding appointments to powerful committees). The ultimate threat is to support another candidate in the primary election with endorsements and party funds. The party whip will operate under the direction of the particular party's leader (called respectively the majority leader or the minority leader).

Explanation:

Hope that this helps! :)

the american colonists were happy with their vicorty, but the french were mad and the french and indians were not alies, and neither were the french and colonist. i think,