NEW YORK, NY.- Richard J. Whalen, who in his diverse career wrote a bestselling biography of Joseph P. Kennedy, the patriarch of the Democratic political dynasty, before joining Richard Nixon’s 1968 presidential campaign as a speechwriter — but who left before the election and wrote a critical book about him — died July 18 in Yorktown Heights, New York. He was 87.

His daughter, Laura Whalen Aram, said his death, at a nursing home, was caused by pneumonia.

Whalen was 27 and working at Fortune when the magazine published his 13,000-word profile of Joseph Kennedy in January 1963. His article described how he had accumulated great wealth and rose to become chair of the Securities and Exchange Commission and then, early in his time as the United States ambassador to Britain, with the war looming, “publicly urged coexistence between the Western democracies and Hitler’s Germany.”

But, the article continued, what he craved more than money was political success for his sons. “While making money,” Whalen wrote, “Kennedy managed to raise three attractive, persuasive sons who come easily to leadership. Wealth made their arrival easier; it didn’t guarantee it.”

By early 1963, his eldest son, John, was the president of the United States; his middle son, Robert, was the attorney general; and his youngest, Edward, was a senator from Massachusetts.

“In a way that goes deeper than ordinary parental pride,” Whalen wrote, “their success is his.”

Whalen soon had a dozen publishers, by his count, asking him to turn the article into a book. He received a $100,000 advance (about $1 million in today’s dollars) from New American Library to write “The Founding Father: The Story of Joseph P. Kennedy” (1964), which preceded by decades other biographies of Kennedy, including David Nasaw’s “The Patriarch: The Remarkable Life and Turbulent Times of Joseph P. Kennedy” (2012).

“What was astounding,” Nasaw said in a phone interview, “was that he had almost none of the documentation that I and other Kennedy biographers have had and he was able to ferret out so much information about this guy and get a sense of the conflicts, controversies and drive that motivated him.”

“The Founding Father” spent 28 weeks on The New York Times’ hardcover bestseller list.

Whalen left Fortune in 1965 to be a writer in residence at the Center for Strategic and International Studies, a bipartisan policy research think tank that at the time was affiliated with Georgetown University. An article that he wrote for the center in 1967, about nuclear defense, attracted the interest of Nixon, who asked him to be an adviser and speechwriter as he sought the Republican presidential nomination.

But Whalen, a conservative, left the campaign shortly after Nixon’s nomination in August 1968. At the time, he attributed his departure to clashes with John Mitchell, the campaign manager, and other aides. But four years later, in his book “Catch the Falling Flag: A Republican’s Challenge to His Party,” Whalen detailed his disappointments with Nixon, including his pledge in March 1968 to end the Vietnam War, presumably swiftly, if President Lyndon B. Johnson didn’t end it by the end of the year.

“This promise, implying a plan to fulfill it, splashed across the front pages and brought the reporters and TV crews rushing back to the Republican side of the New Hampshire campaign, eager for details,” he wrote. “There weren’t any. Nothing lay behind the ‘pledge’ except Nixon’s instinct for an extra effort of salesmanship when the customers started drifting away.”

Richard James Whalen was born Sept. 23, 1935, in the New York City borough of Brooklyn. His father, George, was a textile executive, and his mother, Veronica (Southwick) Whalen, was a bookkeeper.

After earning his bachelor’s degree in 1957 from Queens College, where he studied English and political science, he was hired as a reporter at The Richmond News Leader in Virginia. While there, he wrote about school desegregation and later became an editorial writer, working for James Kilpatrick, the paper’s editor, who was also a nationally known conservative columnist.

In 1960, Whalen left for Time magazine, where, as a national affairs correspondent, he covered the civil rights movement. Soon after that, he moved to The Wall Street Journal as an editorial writer, but in 1962, he returned to Time Inc., where he became a staff writer at Fortune.

Whalen later recalled that Henry Luce, Time Inc.’s co-founder and editor-in-chief, assigned him to write the profile of Joseph Kennedy, a longtime acquaintance of Luce’s. The Kennedys refused to cooperate on either the article or the book that followed.

“They weren’t happy,” Joan (Giuffré) Whalen, Whalen’s wife, said by phone. But, she added, “We were told that Rose Kennedy enjoyed reading the book and marking it up.”

Whalen’s experiences with the think tank and the Nixon campaign led him to other political work. He worked as a consultant and writer for William Rogers, Nixon’s secretary of state, from 1969-70 and as a personal adviser to Ronald Reagan before and during his presidency.

In the late 1960s, Whalen started World Wide Information Resources, which provided his analyses of politics, economics and foreign policy to subscribers, first via telex and then via fax and email. His clients as a lobbyist included Toyota Motor Sales USA, Toshiba America and the Japanese Ministry of International Trade and Industry.

“I’m a free trader who believes deeply that the U.S. market is regulated by the consumer,” he told The Richmond Times-Dispatch in 1987 when asked about his lobbying for Japanese companies while the United States had a large trade deficit. “We are absolutely sure to injure ourselves if we go the protectionist route.”

In addition to his wife and daughter, Whalen is survived by his sons, R. Christopher and Michael; four grandchildren; and a brother, George.

Whalen’s book about Nixon was published in May 1972, a month before the Watergate break-in, which evolved into the scandal that led to his resignation two years later. While promoting the book, Whalen mocked Nixon as a monarch living in a “splendid court” and castigated him for falling short of his promises as a conservative Republican.

“The difference between what your administration has done and proposed to do, and what a Humphrey administration would have done, is not very significant,” he wrote in an opinion article for The New York Times, referring to his Democratic opponent in the 1968 election, Vice President Hubert H. Humphrey.

“I, too, know that you have a philosophy, to which you once privately gave the name ‘conservative,’” he wrote. “Publicly, however, you give your government the label ‘centrist,’ which shifts meaning so often as to be meaningless.”

This article originally appeared in The New York Times.