Every political biographer must decide how he is going to balance the public and private lives of his subject. What is important—John F. Kennedy's compulsive sexual relationships or, say, his handling of the Cuban Missile Crisis? In times past, biographers accentuated the public record rather than private conduct, but we live in an era of unrestrained partisanship and gotcha journalism that affects even the most scholarly writers.

Which explains, I believe, why Joseph Crespino, a professor of history at Emory University, begins his biography of Strom Thurmond (1902-2003) with these incendiary words: "Strom Thurmond is remembered today as one of the great American hypocrites: the firebrand segregationist who had a black daughter." The last page of the epilogue reads: "It is impossible to separate his grandiose acts of segregationist defense—or his later refusal to acknowledge them, much less apologize for them—from the secret of his black daughter."

In between these censorious assertions is a great deal of solid research about a Southern politician who was first elected governor of South Carolina on a "liberal" platform of more education for blacks, who ran for president as a segregationist "Dixiecrat" in 1948, who delivered the longest filibuster in Senate history against the 1957 civil-rights bill and who served in the Senate for a remarkable 48 years, until the age of 100.

Mr. Crespino concedes that "Ol' Strom" mellowed over the years on the issue of race, being the first member of the South Carolina congressional delegation—and the first Southern senator in modern times—to appoint an African-American to his staff. He supported the 1982 extension of the Voting Rights Act and voted for a national holiday honoring Martin Luther King Jr. All of which prompted the head of the South Carolina NAACP to remark: "We don't care what the senator did in the 40s and 50s but how he is representing us [today]." But the author reiterates his theme that Thurmond never apologized for his early positions and that his later actions were always hypocritical. Yet one wonders: How can the author be so certain that Thurmond never expressed regret for his segregationist past, even to a family member or aide?

Is Thurmond only remembered today as "one of the great American hypocrites"? A lot of Republicans are grateful to him for his 1964 switch from the Democratic to the Republican Party. That dramatic transfer of allegiance not only helped Barry Goldwater carry the Deep South in his presidential bid but cracked the Democratic hold on the South and made possible the transformation of the GOP into a truly nation-wide party.

And what of Thurmond's role as political lifeguard at the 1968 Republican National Convention? Richard Nixon was favored to win the nomination, but at the last hour California Gov. Ronald Reagan announced his candidacy, causing conservative delegates to look forward to the prospect of a President Reagan. Thurmond, who had already endorsed Nixon, came to Nixon's rescue and helped to keep wavering Southern delegates from bolting. If Thurmond had not become a Republican, there might well have been no President Nixon—and no Watergate, among other things—but there might have been a President Humphrey.

Mr. Crespino includes the 1964 and 1968 stories in his biography but argues that Thurmond's party switch was racially inspired and served to reinforce the GOP's "Southern strategy" of seeking only white votes. He writes that in his dozens of campaign speeches for Goldwater in 1964, Thurmond emphasized Goldwater's vote against the Civil Rights Act earlier that year and predicted that, as president, Goldwater would salvage "the rights of the individual, the rights of the states." But Mr. Crespino omits that, in the last week of the campaign, Goldwater and Thurmond stood side by side in Columbia, S.C., as the Republican candidate condemned segregation and declared that government must treat "all men as equal in the areas of law and civil order." The speech was broadcast on 87 TV stations throughout the South.

Thumond's political career spanned an incredible seven decades, beginning in the South Carolina Senate in 1933 and ending in the U.S. Senate in 2003. Mr. Crespino describes the senator as "one of the last of the Jim Crow demogogues" and at the same time "one of the first of the post-World War II Sunbelt conservatives." Throughout his 379-page study, he insists racism dominated Thurmond's political decisions.

But what is "racist" about Thurmond's constitutional conservatism, his championing of the New South and its avid pursuit of business and industry, his support of right-to-work laws? Constitutionalism is the main theme of his one and only book, "The Faith We Have Not Kept" (1968). (Incidentally, Mr. Crespino says that I "ghostwrote" the book. "Edited" is the more accurate word; the book relies on Thurmond's speeches drafted by his staff. It was my one and only affiliation with Thurmond, and I was paid by the publisher, who approached me after I had published a biography of Ronald Reagan.)

"The Faith We Have Not Kept" reflects Thurmond's other abiding concern—national security. As a member and chairman of the Senate Armed Services Committee, he endorsed President Reagan's policy of "peace through strength" and insisted that we be adequately armed to defend ourselves against the Soviet Union and other adversaries. Thurmond was an anticommunist early and late, warning in January 1962, for example, that there were Soviet missiles in Cuba, based on information supplied by Cuban exiles.

The last section of Mr. Crespino's work is titled, "Myths, Memories, and Legacies." He sums up by saying that Thurmond was a committed segregationist who only "accommodated himself to the new era." His support of voting-rights legislation and the King holiday was calculated to gain him a reputation "as a GOP elder statesman." Perhaps so, but even Sen. Ted Kennedy appreciated the "new" Thurmond, describing him as "fair to all sides."

Six months after Thurmond's death in June 2003, a retired African-American schoolteacher, Essie Mae Washington-Williams, held a news conference at which she confirmed that her father's name was "James Strom Thurmond." (Her mother had worked for Thurmond's parents.) She and Thurmond had agreed to keep the relation secret throughout his career. No deadbeat dad, he generously supported her, sending her to college and helping put her son through medical school. Mr. Crespino writes: "There was no trace of resentment or injury in any of [Washington-Williams's] public statements; she was the picture of the loyal and loving daughter."

But Mr. Crespino cannot leave it there, referring in the last pages of his book to Thurmond's "moral failings" in his public and private lives. But Strom Thurmond was neither the great sinner depicted by Mr. Crespino nor the courageous saint cited by some Southern conservatives but a practicing politician and shrewd pragmatist who loved the Old South but welcomed the New South, with its voting rights for all citizens. His elections and re-elections over the decades suggest that the majority of South Carolina voters, black as well as white, would accept that judgment.

—Mr. Edwards, the author of "Goldwater: The Man Who Made a Revolution," is a fellow at the Heritage Foundation in Washington.

A version of this article appeared September 1, 2012, on page C7 in the U.S. edition of The Wall Street Journal, with the headline: The Last Dixiecrat.