When John F. Kennedy was elected president in 1960, some alert political observers scrutinized the books written by historian Arthur Schlesinger Jr., then at Harvard, for clues that might reveal what to expect once JFK was in power. Schlesinger was also sensitive to the impact that historical ideas might have on a presidency. He was not displeased when his landmark early work “The Age of Jackson” (1945) was exalted as rationale for the domestic liberal activism of Franklin Roosevelt and Harry Truman. And when Truman was widely vilified for firing Gen. Douglas MacArthur in 1951, the commander in chief was delighted when Schlesinger came to his defense by writing a book, with New Yorker contributor Richard Rovere, called “The General and the President.” While running for president, Kennedy let it be known how much he admired Schlesinger’s three-volume history of the early FDR years, and, after his victory, he appointed the historian to his White House staff.

Sean Wilentz of Princeton is one of the best American historians of his generation. He and Hillary and Bill Clinton are well known to be strong mutual admirers. There is no particular reason to suspect that Wilentz aspires, as Schlesinger did, to enter the federal government. Should Hillary Clinton be elected this November, however, one would do well to revisit Wilentz’s work for a preview of some of the historical rationale that might be deployed by the new president, explicitly or otherwise, in defense of her agenda and approach. For instance, Wilentz’s affinity for happy political combat on behalf of left-of-center goals is consonant with the former secretary of state’s presidential announcement speech a year ago this month. In her remarks, delivered at a rally in New York’s Four Freedoms Park, honoring Franklin Roosevelt, she called her program the “Four Fights.”

Wilentz is by no means a Bernie Sanders Democrat. When Bill Clinton was in the White House, the historian defended the president against charges that he was insufficiently liberal and got him to give the keynote address at a 2000 Princeton conference on the history of progressivism, for which Wilentz also persuaded Schlesinger to deliver a paper. Both Wilentz and Schlesinger testified before Congress in Clinton’s defense during the House Judiciary Committee’s impeachment hearings in 1998. Wilentz has reportedly been in contact with Hillary Clinton during the current campaign.

For those readers eager to be introduced to Wilentz’s work, “The Politicians & the Egalitarians” is a good place to start. Preponderantly drawn from Wilentz’s writing for journals including the New York Review of Books and the New Republic, the book suggests the range of the author’s interests and his command of more than two centuries of American history, addressing W.E.B. Du Bois, the Gilded Age, Lyndon Johnson, Thomas Paine, Thomas Jefferson, John Quincy Adams and Abraham Lincoln. Not surprisingly, he chides Lincoln historians for being overinclined to scoff at “the importance of party politics” in his ascent, noting that “the candor of Lincoln’s language, the ease with which he accurately describes his real vocation, is bracing. He saw no shame in the practice of politics, and experienced no priggish discomfort about what it takes to get great things done.” ...