We assess the influence of moneyed interests on legislative decisions. Our theory predicts that the vote outcome distribution and donation flows in a legislature feature a discontinuity at the approval threshold of bills if special interest groups are involved in vote buying. Testing the theoretical predictions based on two decades of roll-call voting in the U.S. House, we identify the link between narrowly passed bills and well-timed campaign contributions. Several pieces of evidence substantiate our main finding, suggesting that moneyed interests exert remarkably effective control over the passage of contested bills