Are the Ds and Rs really a "party?"

If you think we have two political parties, or three, try to join one. See if you can find an office. Most of the time you can't because there isn't one. If you can, as in an election season, see what it takes to become a "member." Can you get a card? More importantly, can you use this "party" or "membership" to advance a legislative agenda? Ask how you make your voice heard through this "party" to influence public policy.
That's because what we usually call a "party" is really just a campaign. What the media usually calls a "party" is a caucus of like-minded people in the Congress or legislature. It doesn't really engage you, want you or serve your political interest. It just tries to get power and keep power.
The likelihood that Obama or McCain or anyone else elected president will fix what ails you is almost nonexistent on a specific issue.
For example, if you want to change the law, your best bet is the much aligned special interest group, which performs many functions political parties ought to perform. That is, research issues, write and introduce legislation and advocate for policy.
And the special interest group includes you in the process and reflects your views.
It is more accurate to speak of the Democratic or Republican "campaign" than to call them a party. And more effective to turn to a special interest group to pass or stop legislation.
Why else do you think there are so many?