Think about this to get dominated for committees, to get backing, to get Elected long term you have to Follow the Party line. How often do you see Party members vote outside the established parameters of the Party? And if they do what usually happens to them. It happens on occasion if they are well established in their state but it usually comes with ramifications long term.Instead of voting for the candidate that most closely represents your core values, you vote for the party that does. That seems to be irrational, and lacking in intellectual effort.
We have a two party system, winner take all. Once a person is elected Dem/GOP and they want to gain influence and get on committees and wield power they have to dance to the party line they have pledged allegiance to.
You seem to in error believe that one Elected Official has more Power than the Group Cronies that are in Control of the system. I literally gave you two examples of people who stood on their own principles and where ostracized by their party's for those principles.
In short I know once a person is elected their core values are meaningless they will tow the party line 95% of the time its how politics works. I'm not gullible enough to think that Politicians are going to change the system or step outside the Party Power.
The party set's and controls the Politicians much more than you realize.