"If only." Those two words have the potential to lead to hours of discussion, conjecture, speculation and robust debate. For a political junkie such as Jeff Greenfield, those words have inspired a fascinating book. Greenfield, the senior political correspondent at CBS News and a veteran reporter at CNN and ABC, has an impressive political resume that includes stints with Robert Kennedy and New York Mayor John Lindsay. His knowledge of and love for politics is evident to any viewer of his regular television appearances.

Greenfield has selected three events from the late 20th century to form the speculative basis of his book. The first game-changing occurrence is an assassination attempt on John F. Kennedy. In December 1960, Richard Pavlick, a retired postal worker, drove a dynamite-loaded car to the Palm Beach, Florida vacation residence of the President-elect, but his plan was foiled by law enforcement. Greenfield speculates how history might have changed had Pavlick succeeded in exploding his device. A constitutional crisis would have resulted as the Electoral College had not yet voted for the President and Vice-President. In the skillful hands of Greenfield, the hypothetical history reads like actual reporting.

The saga of Richard Pavlick is unknown to many Americans. However, Sirhan Sirhan is recognized by almost all and remains in the news today. This past week, California authorities denied Sirhan parole for the June 1968 killing of Robert Kennedy. THEN EVERYTHING CHANGED speculates on how history might have been different had the murder never occurred. The result, according to Greenfield, is the presidency of Robert Kennedy. In his description of the Kennedy presidency, Greenfield's admiration for the New York Senator is clear. Not surprisingly, in Greenfield's view, the Vietnam War comes to an early conclusion. He is one of many who fervently believe that both JFK and RFK would have dealt with the war in a far different fashion than Lyndon Johnson and Richard Nixon. This theory finds no factual support in history. Disagreement with Greenfield on this point, however, does not detract from his ability to fascinate readers with his ideas.

In the third section, Greenfield begins to push the envelope in a somewhat perplexing manner. The basis for this part of the book is that President Gerald Ford snatches victory from the jaws of defeat in his 1976 election battle with Jimmy Carter. Ford's verbal faux pas regarding Russian domination of Poland never occurs. His momentum continues for the remainder of the campaign, and he emerges victorious despite losing the popular vote. History does teach us that such an occurrence is very possible. Somehow, Ford convinces the Shah of Iran to leave office in the fashion of Hosni Mubarak of Egypt. A moderate government comes to power in Iran, and the Middle East is a more stable region.

Beyond this bit of historical legerdemain, Greenfield has quite a bit more domestic political speculation for the 1980 he has created. The presidency is a campaign between Gary Hart and Ronald Reagan. Hart turns the table on Reagan during the campaign by essentially becoming a younger version of the Great Communicator. It is interesting reading but not very believable.

Throughout THEN EVERYTHING CHANGED, there are wonderful references to changes in the historical landscape and what might have been. Readers will need to pay attention because the depth of their own political knowledge will determine their ability to recognize many of Greenfield's historical bon mots. This is a book that requires close attention; gratefully, its style and readability make the effort an easy chore.