At first we thought the Presidents Club was more a concept than a real community. As we did research and interviewed former presidents, though, we discovered that they regard the club as real and that it has membership privileges, nicknames, unwritten rules and taboos, souvenirs and even a clubhouse — an unmarked town house on Washington's Lafayette Square set aside for the sole use of its members.

This tradition of camaraderie has roots as far back as John Adams and Thomas Jefferson, but it was revived for the modern age by Herbert Hoover, of all people, who suggested the club to Harry Truman at Eisenhower's 1953 inauguration. Today the invitation to join comes even before the new commander in chief takes office. President George W. Bush gathered all the living ex-presidents for lunch at the White House in January 2009 so they could, as Carter told us, "educate President-elect Obama in a nice way without preaching to him."

But club members don't concern themselves only with affairs of state. When ex-presidents get together (which they do more often than you might guess) — at library dedications and White House ceremonies, or at golf games and lunches away from the cameras — they share their reinvention strategies and discuss how to find a new mission, a new metabolism and how to use the influence that remains once they relinquish their power.

The current club includes two 88-year-olds (Bush the elder and Carter) and two who are 66 (Clinton and George W. Bush) — all of whom wrestled for months, sometimes years, with how to change gears after leaving office. Their opportunities and obstacles may be unique, but their strategy can be copied: They sought advice from people they respect, people who understand them. Even the most powerful men in the world don't go it alone.

Next: Why former presidents gravitate to adrenaline-rush exercises. »