Congressman have to balance three things, constituency matters, national interest, and party interests. They must strike a compromise; for example: say the democratic party is trying to pass a motion reducing military spending, which results in several bases being closed. If a democratic congressman has one of these bases in his constituency, which is providing jobs etc. he is very unlikely to vote for the motion, and be have the whip temporarily withdrawn because of it. Therefore he will either vote against the closure, or abstain from the vote, and will almost certainly appeal to the relevant committee to change the bill before the second reading.
Congress is influenced by money for campaigning, however normally this money comes from organisations and PAC's, for example the AARP. However the money does not come in the form of a bribe, with the AARP, they send out a questionaire to candidates, and if they feel the candidate represents their interests, they will give them money for campaigning. PAC's are formed to combat individual donors and big business, they are essentially a pool of money which represents certain interests.
Also, the fact that congress doesn't have a proportionate number of people with down syndrome or paraplegics, does not mean that it is not representative of the disabled. Nor does it mean women, african americans, or latinos are unrepresented. A criminal lawyer does not have to be a convicted felon to best represent one in court, they just have to be a good lawyer, and a similar thing applies to congress.
Finally, constituency lines are drawn up by the state, the federal government has no control of this, and what's called "gerrymandering" is an issue. These constituencies often favour the republican party, but many democrats are favoured as well, and in this sense it can make congress more unrepresentative. However it's impact is rather small, and is unfortunately unlikely to be stopped altogether because it requires revoking states rights.
Both political parties represent different groups. For example, most women identify with the democratic party, and they are therefor represented by it. The same goes for other groups, including people of different socioeconomic classes. As for people who are independent, they have opinions on certain issues too, and both sides of those issues are represented by one party or another.
One Congress's many jobs is to represent the best interest of the American public. Some of the laws that are being passed make me believe that they could be doing what is in the best interest of their pocketbooks. When other countries come to the United States, those we choose for office represent how they view us.
There are no retarded people in Congress. This goes to show you that people with retardation are not properly represented. Poor people are also not properly represented either. There is virtually nobody in politics that were born extremely poor and are still extremely poor. Congress is mostly spoiled kids playing out their fantasy of being important.
Congress is not representative of the American public due to the method of dividing districts within states for the house, as well as the demographics and backgrounds of most representatives.
Congressional districts are divided inconsistently within states, with politics biasing where the lines are drawn - further reinforcing whichever party is in charge of drawing the lines and encouraging a system that elects representatives that don't represent the constituents as a whole.
The demographics of Congress also do not reflect those of the American public - there's a disconnect between the proportions of women and minorities in Congress compared to the American public. Without having women and minorities represented appropriately, Congress can not effectively take their viewpoints and concerns into account when making decisions.
Congress is supposed to represent the people, but money has tainted the system. Instead of keeping their constituents in mind, most elected represented spend their time trying to raise money for reelection. This gives the people who fund political campaigns more power than what they should have. Campaign finance reform is truly needed to address this problem.
The government is a representative republic not a true democracy. As such the representatives due what they think is best not necessarily what the people want. They are also beholding to the sources of campaign funds and can and will pass laws which benefit those who benefit them with little regard to the cost.