I'm sure every Congressperson rides the border between:
- Personal morals (i.e. voting against gay marriage or evolution because their religion dictates it)
- Pandering to corporate interests for campaign money (or votes in the case of strong unions)
- Supporting their constituents (or at least appearing to). This can take the form of pandering to corporate interests so that said corporations open up their new offices within said Congresspersons constituency (i.e. bringing new jobs into the area!). It can also take the form of voting on crap laws to look 'tough on crime' or 'tough on child porn' or whatever.
I doubt very much that many of the people in Congress see it as a 'power grab' even if that is essentially what it is.