The 2010 TIME 100

In the Senate, Arizona's Jon Kyl has built a reputation for his encyclopedic knowledge of domestic and foreign policy, and his hard work and leadership. Few people have his command of policy, his knowledge of its nuances or his grip on how they fit together. This is why so many of his Senate colleagues look to him for policy advice. Kyl, 68, is a principled conservative who knows what is attainable. He believes in the wisdom contained in a sign on President Reagan's desk that said, "There's no limit to what a man can do or where he can go if he doesn't mind who gets the credit."

Jon Kyl is a great persuader. As minority whip, the No. 2 position in the Senate Republican leadership, he is responsible for rallying his Republican colleagues for key legislative votes. What is unique is his single-minded focus on convincing them that a particular vote is in the best interests of their state and the nation. Jon demonstrates continually that the essence of Senate power is the power to persuade.

McConnell is the Senate minority leader

TIME 100 Social-Networking Index: 2,696