And what happens when that politician votes for X but 90% of his actual constituents don't support it? He loses the next election and is unemployed. The rich donor no longer needs him.
So the politician must make sure that his vote matches what his constituents want otherwise he's out of office the next term and there's no reason for the rich donor to give him any more support.
As I said in my last post, this assumes a certain type of issue. 99% of voters don't give a shit whether or not online poker is legal or not. So Sheldon Adelson buying votes to ban online poker isn't going to affect a candidate's re-election chances.
Yes, you are correct that if Adelson went to a GOP candidate and said "if you don't become pro-choice, pro-Obamacare, anti-war, pro-social services candidate, I'm not going to support you", then that GOP candidate wouldn't swap on all those issues. He'd lose his voting base.
And don't forget, we're not talking about money the politician gets to use for personal reasons. It's money that goes to buy his campaign things it needs. So the politician isn't getting rich here. To get rich...he needs to say elected and the rich donor can't provide that.
The donors money helps them get elected.
Sure he can. But then it's disclosed and the opposition can start attacking those politicians as being bought by the rich donor. Credibility is shot and re-election for those politicians becomes more difficult.
How is credibility shot when they're basically all doing it?