One of the fascinating things about Richard Aldous’s book about historian-partisan Arthur M. Schlesinger Jr. is its composition. Schlesinger lived to be 89, dying an enviable death of a heart attack in a Manhattan steakhouse in 2007, but only a very few of the 389 pages in Aldous's book concern the 39 years between 1968 and Schlesinger's death.

That is the year the party of the midcentury Democrats fell victim to murder — in the killings of Martin Luther King Jr. and of Robert F. Kennedy — but also to suicide, in the rise of the forces of pacifism, moral equivalence, and identity politics that sadly control it today.

In his duality, Schlesinger cherished two things: big personalities and liberal politics. He acted as aide to three politicians, presidential hopefuls Sen. Adlai Stevenson of Illinois and Sen. Robert F. Kennedy of New York and former President John F. Kennedy, writing books on the two Kennedys after they died. But his zeal to present his heroes as successful and liberal made him present them as both more liberal and more successful than they were in reality, either ignoring some of their actions or curtailing his efforts in time.

With President Franklin D. Roosevelt, he devoted three books to his first term and the crises before it, but he came to a halt at his first re-election, as with that historic and landslide election the good times had come to an end. The groundbreaking measures all were behind him and ahead were the court-packing debacle, stalled growth, and a brutal rebuke in the ’38 midterms. Also ahead was the war that would make him immortal, but as the head of a bipartisan war coalition, a subject that Schlesinger would find less appealing. As Aldous writes, he dropped FDR after reaching the ’36 blowout and never wrote of him again.

Similar editing was done with the JFK saga, making a try at likening the transfer of power in 1960 to that from Herbert Hoover to Roosevelt, with a failed and exhausted older Republican handing the reins to a vital young Democrat, brimming with big and progressive ideas. But Dwight D. Eisenhower was hardly a failure, and he and Kennedy were actually not far apart on most major issues, having been part of the famous Cold War consensus since they first entered politics. The transition story was the peaceful torch-passing of pragmatic centrists, not a dramatic reversal of course. As Aldous quotes Ira Stoll, "Kennedy’s tax cuts, his domestic spending restraint, his military buildup, his emphasis on free trade and a strong dollar, his foreign-policy driven by the idea that America had a God-given mission to defend freedom, both make [Kennedy] by the standards of his time and our own a conservative." What FDR and JFK did share was the "God given mission," which did not fit within party lines.

The problem for Schlesinger in the years after Robert Kennedy was that, in the late 1960s, the Democrats ran out of big men. The midcentury party was teeming with huge, flawed, but oversized people of consequence, which made for good policies and really great reading. Schlesinger seemed to expect that to continue, but instead it suddenly ran dry. By 1969, FDR was a memory; Jack and Bobby Kennedy were dead; Lyndon B. Johnson was broken by war and his vice president, Hubert Humphrey, broken by Johnson. In their place would come clueless dweebs like former President Jimmy Carter and presidential hopefuls former Massachusetts Gov. Michael Dukakis and former Secretary of State John Kerry; or embarrassments like former Colorado Sen. Gary Hart, former Massachusetts Sen. Ted Kennedy, former North Carolina Sen. John Edwards, and former President Bill Clinton, about whom Schlesinger would make the cringe-making comment that "gentlemen" lie about sex all the time.

Faced with this, Schlesinger could do nothing more than retreat to academia and relish with his social life, which he enjoyed greatly. No one could blame him at all.

Noemie Emery, a Washington Examiner columnist, is a contributing editor to The Weekly Standard and author of "Great Expectations: The Troubled Lives of Political Families."