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ny junior senators waste away in the shadow cast by a giant senior colleague. But in just two terms, Arizona's No. 2, Jon Kyl, 63, has blossomed in the shade of John McCain. As head of the Republican policy committee, the ultraconservative Kyl is in charge of shaping the Republican agenda in the Senate on everything from abortion and judicial appointments to national security and tax cuts. He has succeeded by mastering a tactic that is crucial in a body in which any one member can bring the place to a halt as a ploy or out of pique: subterfuge.

America's Best Senators Those who do, and don't, make a difference in the U.S. Senate The Best Senators Thad Cochran Kent Conrad Dick Durbin Ted Kennedy Jon Kyl Carl Levin Richard Lugar John McCain Olympia J. Snowe Arlen Specter The Worst Senators Daniel Akaka Wayne Allard Jim Bunning Conrad Burns Mark Dayton From the TIME Archive Nov. 5, 1979 The Kennedy Challenge More than a quarter century ago, TIME covered the presidential campaign of Senator Ted Kennedy, "the last of the Kennedy brothers, the youngest, the most vulnerable, the most thoroughly political"

Last November, for example, Senator Lindsey Graham of South Carolina proposed a controversial amendment barring U.S. courts from hearing cases brought by prisoners in the war on terrorism. It turned out that Kyl was behind it, having worked on the language for months and having assigned his staff to help write the final bill. But "it was a situation where it was best handled by Lindsey," Kyl says delicately, pointing out that Graham had the credibility of a military lawyer and a centrist. When urgent legislation to respond to Hurricane Katrina bumped Kyl's long-sought goal of a vote on abolishing the estate tax last fall, Kyl quietly worked to get it back on the Senate agenda by recruiting Alabama Senator Jeff Sessions in an unsuccessful attempt to find victims of the disaster who would be paying the tax. And although he denies it, G.O.P. aides say that when Harriet Miers was nominated to the Supreme Court last October, Kyl and his staff led a behind-the-scenes effort to undermine the nomination.

As the Miers fight showed, Kyl does not always find himself on the same side of the battlements as President Bush. The Senator was a leading opponent of the immigration reform compromise backed by the President that collapsed earlier this month. When the Senate returns from recess next week, the Judiciary Committee will take up the immigration debate again. Watch for Kyl to play a pivotal role—if perhaps not the most conspicuous one. "You can accomplish a lot if you're not necessarily out in front on everything," he says.