"2002 shortly after the lawmaker took action favorable to Abramoff's tribal clients."
Abramoff is a lobbyist whose financials are based not on what favors he can get from politicians but on what favors people believe he got from polticians. Oddly enough, it gives him dual incentives to declare his ability to commit bribary to his clients while denying the claim to those upholding the law.
That being said, if Dorgan was going to "urge fellow senators to fund a tribal school program Abramoff's clients wanted to use," which, given a) the school was in North Dakota (I believe), b) the priority of education is a mainstream liberal cause, and c) Dorgan has a lot of North Dakotans as constituents, it seems that if Dorgan was acting noncorruptively, his actions would have been the same.
In my article in the Connecticut Public Interest Law Journal, "The Transparency Myth", I note that lawmaker's actions can be derived from the formula bx + px + cx, in which b equals his burkean motivators (those things he does because he believes they are right), p which eqauls his public choice motivators (those things he does because it makes his constitutents want to vote for him), and c which equals his corrupt motivators, which is what campaign finance law is meant to curtail. If his actions can be understood as a function of bx + px, then that they can also be understood as a function of cx is not evidence of corruption.
Otherwise, then every Senator would have to resign. The simple fact is that, for noncorrupt reasons, self interested individuals give money to candidates whose interests coincide. While this may be problems of inequality in the system (those who support the wealthy will be better funded), it is NOT corruption. Thus, the NRA gives money to those who have voted in the past for the NRA interests, ADM gives money to Iowa legislators who, in order to attract votes, obtain farm subsidies, and unions give money to those who fight to have union laws passed.
Jack Abramoff has (very likely) violated some laws, including bribery, as defined as making politicians vote in ways other than they would for the purposes of obtaining money or other things of value (for themselves and/or their campaign). But this does not make everything that Jack Abramoff done as a lobbyist illegal, nor mean that all his contributions were for the purpose of subverting the law.
The article which explains this theory can be found at Lexis or Westlaw using the citation 4 Conn Pub Int L J 308, or at
http://www.law.uconn.edu/...