During the decade in which F.D.R. improvised the New Deal (much to the young Reagan’s admiration), Willkie evolved into its foe by virtue of his instinctive libertarian sympathies and his professional position. Roosevelt’s Tennessee Valley Authority, through which the government got into the business of providing hydroelectric power, presented a mortal threat to Commonwealth Southern. Lewis does a fine job outlining the six-year war between the Administration and the holding companies, balancing the “orthodox verdict” of history—Arthur Schlesinger, Jr.,’s rhapsodic glimpse of “new life from the foaming waters of the river to the farthest corners of the valley”—with Willkie’s view of a project that “waters five states and drains the nation.”

Throughout Roosevelt’s first two terms, Willkie debated, testified, and litigated against the T.V.A.’s existence. His principal day-to-day adversary was David E. Lilienthal, seven years younger and equally brilliant, one of the Authority’s three directors and later the first head of the Atomic Energy Commission. Lilienthal’s seven volumes of published journals, written between the late nineteen-thirties and the early eighties, provide a distinctly mixed view of Willkie on his way up: “proud as the devil”; “too fast on his feet to be very dependable on any issue”; “a terrifically vital personality,” but prone to bullying theatrics.

Less frequently, Willkie tangled with Roosevelt himself. In these meetings, Lewis writes, the Oval Office would be filled by “two outsized egos puffed up like roosters. ‘Mr. Willkie, I am one of your customers,’ the president bantered. ‘We give you good service, don’t we?’ ” Willkie replied. (The business executive found F.D.R.’s charm to be “greatly exaggerated,” while Harold Ickes, the President’s Secretary of the Interior, sized up Willkie as “a simple barefoot Wall Street lawyer.”) Things between the two of them got worse after 1937, as the Second New Deal took a generally more radical approach than the first. But even after voting for the Republican Alf Landon, in 1936, Willkie remained a Democrat; he “still saw himself as Herman’s son.”

His moderation contributed to his allure and credibility as a foe of Roosevelt. Much of the era’s print-media establishment—the New York Herald Tribune, the magazines of Henry Luce, the myriad publications of John and Gardner Cowles—began showcasing Willkie. In January, 1939, the Supreme Court ended the war between the T.V.A. and Commonwealth, mostly on Roosevelt’s terms, but with Willkie ultimately accepting a settlement check for $78.6 million (worth eighteen times that today) from the abashed hands of David Lilienthal.

Media puffery turned pointedly Presidential in the early months of 1939, prompting Lilienthal to write in his journals that Willkie had been “nominated by the magazines.” There was, however, also a political apparatus at work: the liberal Republican machine in Connecticut, led by Governor Raymond Baldwin, mobilized on Willkie’s behalf, and Oren Root, Jr., a young Manhattan lawyer, began a “petition drive among Ivy League graduates” that quickly secured two hundred thousand pedigreed signatures. Theodore Roosevelt’s daughter, Alice Longworth, a board member of America First, wasn’t far off the mark in saying that Willkie’s candidacy sprang “from the grass roots of a thousand country clubs.” The Party’s alternative choices seemed either as dry as dust—Senators Arthur Vandenberg and Robert A. Taft—or too green: the skyrocketing New York crime fighter Thomas E. Dewey was only thirty-eight, and Harold Stassen, the “boy wonder” governor of Minnesota, was five years younger.

Even so, Willkie’s ascent was implausible enough for Lewis to pronounce the candidate not merely a dark horse but a unicorn. Some of his detractors saw collusion between his backers and British intelligence agents. Was the chairman of the Convention’s Arrangements Committee, Ralph Williams, really the victim of a heart attack, or was he poisoned—killed so that the galleries could be packed with the supporters of a candidate (“We Want Willkie!”) who wished for the U.S. to aid Britain in its resistance to Hitler? Was the microphone of the decidedly anti-Willkie Herbert Hoover cut off during his speech? The whole chaotic convention story was nicely told a dozen years ago by Charles Peters, in a book called “Five Days in Philadelphia.” Willkie made it on the sixth ballot and chose Senator Charles McNary, a noninterventionist from Oregon, as his ticket-balancing running mate. Lewis notes the “unstable combination” of internationalists, isolationists, and “pragmatists” that went forth to campaign. And yet one can’t judge this amalgamation to be any less stable than the New Deal coalition of union labor, religious minorities, African-Americans, and Southern segregationists that had twice delivered the White House to Roosevelt.

With war threatening and, a decade into the Depression, the economy still precarious, Willkie did not claim that he alone could fix things. It was Roosevelt’s supposed indispensability, implied by the very idea of his running for a third term, that gave the challenger his best leverage. But Willkie faltered, getting out on the stump later than he should have, and then talking himself hoarse. Republican regulars complained of Roosevelt’s early plans to arm Britain through a lend-lease program; Willkie then overcompensated for his own interventionism by calling Roosevelt a warmonger. The President serenely told voters, “Your boys are not going to be sent into any foreign wars.”

Lewis says that Willkie offered “the intelligent businessman’s long-overdue synthesis of the New Deal at its best and the liberated market economy at its most productive,” but most voters already understood the New Deal to be a synthesis of the free market and government regulation. Willkie’s biggest problem was the perception that he offered what a later generation of movement conservatives would deride as an echo instead of a choice. At the other end of the spectrum, Norman Thomas, running once again in 1940 as the Socialist candidate, pointed out that Willkie “agreed with Mr. Roosevelt’s entire program of social reform and said it was leading to disaster.”

“Uh, back to Sea World?”

Newsreel clips available on YouTube capture the charm of what Lewis calls “this large, disheveled, cerebral male.” Willkie’s movement is casual, and his gruff, often gravelly voice can bring to mind Wallace Beery playing Long John Silver. One gets several revealing glimpses of him in Richard Norton Smith’s 1982 biography of Thomas Dewey, Willkie’s rival in the primaries: “Willkie read four books a week, and he never learned to drive, because his restless mind refused to concentrate on the road ahead.” One interviewee told Smith that she could “still see Willkie, late for a speech, running through the library, raincoat over his shoulder, half done up, like his mind.” The rapid, unsustained nature of his thoughts made him, as Lewis acknowledges, a better debater than an orator. He often mislaid his papers on the way to a lectern or a meeting. The novelist Booth Tarkington, another Hoosier, insisted on Willkie’s genuineness, whereas Irving Stone saw “a man with a great potential for good and an equal potential for confusion and opportunism.”

Like Roosevelt, Willkie wasn’t made for monogamy. Edith Wilk Willkie, his wife since 1918, was frail and devoted, determined to endure a long marriage that burned out early. (The Tracy-Hepburn political comedy “State of the Union,” from 1948, borrows elements of the couple’s life.) In the late thirties, Willkie embarked on a serious, lasting affair with Irita Van Doren, the book critic of the Willkie-boosting Herald Tribune. Breezily flagrant about the romance, Willkie once conducted a press conference in her Greenwich Village apartment. He should have had little to fear in the matter from Roosevelt, whose own history of philandering made for a political balance of terror. But Lewis, in quoting Roosevelt’s discussion of the Van Doren affair—from one of his Oval Office tapes—leaves out the part where the President says that Democratic operatives “down the line can get it out,” even if “we can’t have any of our principal speakers refer to it.”

The campaign turned strident on both sides, and the Willkies were jeered and pelted with rotten eggs in more than one city. Having won two previous elections in landslides, Roosevelt and his advisers were nevertheless worried this time. But on November 5, 1940, Willkie came away with just ten states and forty-five per cent of the vote. He appeared to be a phenom who had had his one shot and been speedily extinguished. Willkie himself refused to see it that way. The last chapter of his life, stretching over the next four years, turned into what Lewis calls a pas de deux with Roosevelt—a frustrating, sometimes treacherous, but highly consequential relationship.