AIPAC:How the Israeli lobby works in the United States

"Skirting laws, AIPAC's largesse was provided with heavy expectations. A Congressman knew that if he did not vote in favor of Israel in the next Bill, his perquisites would be dropped. Moreover, it was evident that support for his re-election bid was either guaranteed, or - if not pro-Israel enough - not only withdrawn but an organized campaign would ensue to make sure he was defeated."

http://www.councilforthenationalinterest.org/news/israellobby/item/2193-how-the-israeli-lobby-works-in-the-united-states