The “Iron Triangle” is a way of talking about how Washington works. It is simplistic but very useful as a teaching tool. Here is a visual of the triangle. The concept suggests that actual policy, especially when it comes to expenditures and revenue, is negotiated out by interest groups; congress (specifically in committees); and the bureaucracy.
With the President’s budget now out many people simply think that will be the budget but nothing can be further from the truth. The old saying goes “The president proposes but Congress disposes is true. A good example is the cuts in the State Department. One of the first thing that happened was a group of retired generals signed a letter opposing the cuts. They might be taken as the “interest group” but other interest groups will weigh in such as Universities who received State Department grants; the Foreign Service Officer association; the retired Foreign Service Officer association; etc.
How will they try to influence the process? They are respected figures and they know the people both in Congress and in the Bureaucracy who can provide information; make arguments; craft new figures; and save programs.
Congressmen are motivated by re-election but also by pursuing policies they believe in and rising in the organization of Congress. Their job is easy when all of that comes together. For example, a Congressmen from a conservative district who is interested in cutting departments and has the support of the speaker. More interesting are those individuals who become “cross pressured” when the Speaker or the President (or their own beliefs) are at odds with their Constituent’s wishes. Here is a group of Congressional Districts won by Clinton but held by a Republican. They will be very interesting to watch in the next few weeks. I note that Cong. Issa of California, who is very conservative, has called for a Special Prosecutor.