Big contributors want something for their money. At its most benign, they want access, the ability to have their side heard whenever there is the possibility that legislation might affect their industry. Far less benignly, they want more — they want to know that their bidding will be done.

It can be subtle, this influence. “Maybe it’s the amendment that does not get introduced in committee because the congressman knows that it is not in sync with the desires of his money patrons,” said Representative. John Sarbanes, Democrat of Maryland, who has focused much of his legislative effort on campaign finance reform. “The donation is lingering somewhere in the atmosphere. It’s human nature.”

Of course it can be not so subtle, too. “On any given Wednesday night in Washington,” says Nick Penniman, the executive director of Issue One, which is dedicated to reducing the influence of money in politics, “you’ll have a member of, say, the finance committee, standing in the board room of a lobbyist’s office, surrounded by bank lobbyists. At some point, someone will hand a staffer an envelope with the checks in it, and the congressman will have raised $100,000 in 45 minutes. And they know exactly who was responsible for putting it together, and whose phone calls therefore need to be returned.”

Penniman makes a distinction between “ideological givers” — donors like the Koch brothers, motivated by the chance to get like-minded people elected — and “transactional givers,” those who donate because they expect something concrete in return. “These are folks who give just as generously to both sides of the aisle.” Sarbanes agreed: “Big money wins regardless of which party wins the election.”

“In fact,” he added, “the more money that is spent, the greater the dependence that is created.”

There are two other reasons big money is corrosive to our politics. One is that the need to raise money has become close to all-consuming. The current issue of Esquire magazine — which has a nifty package of articles about what is wrong with Congress and some suggestions for how various problems might be fixed — quotes Donna Edwards, Democrat of Maryland: “It’s a never-ending hustle. You get elected to this august body to fix problems, and for the privilege, you find yourself on the phone in a cubicle, dialing for dollars.”