The problem with political bribery is that it's very hard to prove -- because it's so similar to what every politician does every day. Why does any organization -- whether it's the teachers' unions or Microsoft -- give $$ to politicians? With the expectation that the donation will make it more likely that the politician will support their position. That is perfectly legal. Improper bribery is the simply the formalization of that expectation into an explicit understanding.

Few politicians are stupid enough to cross that line, if only because it's unnecessary to do so. There are plenty of ways for a politician to signal that he'd be willing to consider voting for something, whether it's legislation favorable to Indian casinos or teachers' unions, without entering into a formal quid pro quo agreement. So I wouldn't get too excited yet.