Lead: In January 1972, Richard Nixon was inaugurated for a second term after winning one of the greatest triumphs in U.S. presidential history. Then it all came crashing down.

Intro.: A Moment in Time with Dan Roberts.

Content: Defeating an incumbent President of the United States is tough. It can be done, as Herbert Hoover, Jimmy Carter and George H.W. Bush found to their regret, but it is no easy task. Circumstances, political and otherwise, have to work perfectly to the advantage of the challenger.