Rep. Ed Perlmutter shakes hands with Carlyn Meyer and other members of the groups J-Street and MoveOn.org as they urge him to support the Iran nuclear deal at an event in Denver. J-Street plans to spend about $5 million on ads in this fight, which is vastly dwarfed by the $20 million to $40 million from groups like AIPAC that oppose the agreement. Jason Bahr/Getty Images hide caption

itoggle caption Jason Bahr/Getty Images

The amount of money spent on Capitol Hill is way more than small change — but the impact of that money is a little murky. Here, the U.S. Capitol is reflected in a fountain full of coins on Election Day this year. Mark Wilson/Getty Images hide caption

itoggle caption Mark Wilson/Getty Images