Fred Greenstein, a leading scholar of the American presidency who helped resurrect Dwight D. Eisenhower’s political reputation and went on to analyze the leadership styles of 30 of the 44 individual presidents, died Dec. 3 at his home in Princeton, N.J. He was 88.

The cause was complications from a form of Parkinson’s disease, said his wife, Barbara Greenstein.

A Princeton University politics professor from 1973 until his retirement in 2001, Dr. Greenstein specialized in political psychology, getting inside the heads of politicians, the adults who vote them into office, and grade-schoolers who — according to his research — are far more trustful of heads of state than their parents.

He spent the bulk of his career focused on presidents, having been inspired by Richard M. Nixon’s downfall in the Watergate scandal to explore their personalities and leadership styles. “Why, I wondered, was that politically gifted chief executive, whose first term had resulted in such dramatic achievements as the opening to China and detente with the Soviet Union, succumbing to what was plainly a self-inflicted political disaster?” he once recalled thinking.

Dr. Greenstein effectively spent the next two decades working out an answer, broadening his research to develop a systematic approach to evaluate each president’s performance in office. While he maintained a lower profile than historians such as Doris Kearns Goodwin or Jon Meacham, he became a reliable source for journalists seeking context on the potential presidential campaign of Colin L. Powell (his knack for remembering names reminded Dr. Greenstein of Hubert Humphrey) or the impeachment of Bill Clinton (“He’ll be remembered as a kind of low-achieving Nixon”).

Dr. Greenstein’s work centered not on the policies of particular presidents or the relative merits of their agendas, but on their effectiveness as leaders — on the means they employed, rather than the ends they sought.

Taking advantage of newly declassified archival materials, including telephone transcripts and memo drafts, he initially focused on Eisenhower, the World War II hero whose two-term presidency from 1953 to 1961 was seldom given high marks.

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While critics depicted Eisenhower as aloof and absent-minded, leaving important daily matters to Sherman Adams, his chief of staff, Dr. Greenstein’s book “The Hidden-Hand Presidency” (1982) argued that Eisenhower exerted almost Machiavellian control from behind the scenes.

“This really was a major re­interpretation of Eisenhower, one that went against just about everything scholars had done portraying him as a lazy leader who delegated everything to his staff,” said R. Douglas Arnold, a Princeton professor of politics and public affairs. “Scholars and journalists like to do rankings of presidents, and after that, Eisenhower was drifting up considerably.”

Dr. Greenstein went on to conduct similar — if shorter — studies of each modern president from Franklin D. Roosevelt to Clinton, which together formed his 2000 book “The Presidential Difference,” later expanded to include sections on George W. Bush and Barack Obama.

The work sought to form a kind of middle ground between that of political scientists Richard E. Neustadt, who emphasized the importance of political skill in his book “Presidential Power and the Modern Presidents,” and James David Barber, who examined the psyches of American heads of state in “The Presidential Character.”

For Dr. Greenstein, six qualities were essential to shaping a president’s success or failure: public communication ability, organizational capacity, political skill, vision of public policy, cognitive style and emotional intelligence.

“For journalists,” said the late Washington Post reporter David Broder, “it is a great checklist as to what we ought to be — but probably are not likely to be — looking for in a presidential candidate.”

As he did for his work on Eisenhower, Dr. Greenstein immersed himself in archival materials, while also interviewing associates of the presidents. As in the case of Gerald Ford, Jimmy Carter and Clinton, Dr. Greenstein met with some of his subjects. Political experience hardly ensured success, he found, and while cognitive ability was important, it was not entirely essential.

What seemed to matter above all was that elusive quality of “emotional intelligence” — “the president’s ability to manage his emotions and turn them to constructive purposes, rather than being dominated by them and allowing them to diminish his leadership.”

Lyndon B. Johnson, Carter, Clinton and Dr. Greenstein’s scholarly muse, Nixon, all “had impressive intellects and defective temperaments,” Dr. Greenstein wrote, adding: “All four presidential experiences point to the following moral: Beware the presidential contender who lacks emotional intelligence. In its absence all else may turn to ash.”

Fred Irwin Greenstein was born in the Bronx on Sept. 1, 1930. His father was a buyer for a department store in Portland, Ore., and his mother was a homemaker. Neither was interested in politics, Dr. Greenstein said, but a “very politicized” aunt piqued his interest in public affairs. By the time he was 6, he was fighting with a classmate who dared to support Kansas Gov. Alf Landon, the Republican candidate, over the Democratic incumbent, Roosevelt.

The family moved to the Chicago area when Fred was a teenager, and he graduated from high school in Highland Park, Ill., planning to become a journalist. Dr. Greenstein graduated in 1953 from Antioch College in Yellow Springs, Ohio, but after being drafted into the Army, he decided to return to school and received a doctorate in political science from Yale University in 1960.

“Growing up in the World War II period and the beginning of the Cold War, I was struck by the elements of emotion in politics, particularly irrationality,” he told the New York Times in 2000. “All this sort of led me to be interested in the psychological aspect of politics.”

For his doctoral thesis, published as “Children and Politics” (1965), he surveyed 659 students in fourth through eighth grade in New Haven, Conn., asking them about their political beliefs, or lack thereof.

The book was one of the first major works of political socialization (the study of how individuals acquire political views and values), according to Arnold, and Dr. Greenstein repeated his children’s surveys in the late 1960s and early ’70s — finding, much to his surprise, that children consistently maintained positive views of the president and other authority figures.

Dr. Greenstein taught at Yale and Wesleyan University before joining Princeton, where he served as chairman of the politics department and directed the Research Program in Leadership Studies at the Woodrow Wilson School of Public and International Affairs.

Survivors include his wife of 61 years, the former Barbara Elferink of Princeton; three children, Michael Greenstein of West Newton, Mass., Amy Greenstein Dahn of South Orange, N.J., and Jessica Greenstein of New Paltz, N.Y.; a sister; and six grandchildren.

With John Burke, one of his students, he wrote “How Presidents Test Reality” (1989), which analyzed Eisenhower’s decision not to commit American troops to Vietnam and Johnson’s subsequent decision to do otherwise.

Continuing to write into retirement, he also applied his six-point leadership rubric to earlier presidents in “Inventing the Job of President” (2009), “Presidents and the Dissolution of the Union” (2013) and — with a co-author, Dale Anderson — “Presidential Performance in the Progressive Era,” which his wife said he had nearly completed just before his death.

“He could be so dispassionate about his subjects,” Barbara Greenstein said in a phone interview. “Even when I hated a president, he was very analytic and wouldn’t take sides.”

Indeed, in “The Presidential Difference,” Dr. Greenstein wrote: “A story is told about an airman who escorted Lyndon Johnson across a tarmac in Vietnam, saying, ‘This is your helicopter, Mr. President.’ ‘They are all my helicopters,’ Johnson replied. When I am asked which president I admire most, I have come to say, ‘They are all my presidents.’ ”