By Gene Lyons
Updated August 20, 1993 at 04:00 AM EDT

Analysts debate the usefulness of psychodrama as a therapy. Scholars argue the merits of psychobiographies of historical figures like Hitler and Stalin. But it took Joe McGinniss, author of The Last Brother, to see the commercial possibilities in churning out what can only be called a psychomelodrama about Sen. Edward Kennedy of Massachusetts.

Understood purely as fiction, The Last Brother combines the bombastic political rhetoric of Allen Drury’s Advise and Consent with the crude characterizations of a Harold Robbins saga. For readers indifferent to the distinction between fact and fantasy — or willing to believe anything rotten about a politician — The Last Brother makes for, as they say, a helluva read.

If you’ve been living on the moon, that is. For readers of an age to recall vividly the assassinations of President John F. Kennedy in 1963 and Sen. Robert F. Kennedy in 1968, the experience is more like watching the ultimate Geraldo show.

Except it’s even worse than that. Refused cooperation by the senator and his cohorts, McGinniss has admitted making up dialogue and putting thoughts in his subject’s head. ”This is my view, and perhaps mine alone,” he rationalizes in a self-serving epilogue, ”of what life might have been like for Teddy.” This after 600-odd pages of conspiracy theories and scandalmongering that make the mildly paranoid distortions in Oliver Stone’s film JFK resemble Holy Writ.

The Last Brother is a book in which ”what if” becomes ”maybe,” then changes into ”certainly” without a shred of proof in between. Indeed, so smoothly does McGinniss tell the tale that it’s almost enough to set a reader wondering about some of those too-perfect quotes in his first book, The Selling of the President, 1968, not to mention his dramatic discovery of the incriminating evidence in convicted killer Jeffrey MacDonald’s condominium in his true-crime classic Fatal Vision — a book previously much admired. Curiosity notwithstanding, to buy this book is to be an accessory to a literary felony. F