David Koch underwrote both old-fashioned charitable causes, such as the David H. Koch Center for Cancer Care, and the conservative movement, reshaping U.S. politics.
Diane Bondareff/Invision for Koch Industries/AP
Democrats say they're focused on the Koch brothers because, they allege, Republican candidates are doing the billionaires' bidding. Republicans say Democrats are desperate. David Koch (above) is chairman of Americans for Prosperity.
Phelan M. Ebenhack/AP