The newest book from David McCullough, at the National Portrait Gallery in 2011, is a collection of talks he has given over the past 30 years.

NEW YORK — David McCullough, worried about a president he calls “a cloud” on the American horizon, knows the consolations of history. “We've been through much harder times than we're in now,” the Pulitzer Prize-winning author said during a telephone interview. “Yes, we have had problems and have had dishonest and evil people in positions of responsibility. But we have overcome those challenges and we're often better for it.”

McCullough, 83, had for decades been nonpartisan in his public life. He has praised Democrats (John Kennedy) and Republicans (Dwight Eisenhower) and hesitated to directly criticize a sitting president. His history of the Panama Canal, “The Path Between the Seas,” was cited by members of Congress from both parties as they deliberated over the Panama Canal treaties, approved in 1977.

“When I was a witness to the great debate over the Panama Canal treaties, I saw Congress at its best,” he said. “I saw people crossing party lines when they realized it was the best thing to do.”

McCullough's latest book is “The American Spirit,” a collection of talks he has given over the past 30 years. Known for such best-sellers as “John Adams” and “The Wright Brothers,” McCullough also is a popular speaker, in demand at colleges, historical societies and political gatherings, including a joint session of Congress in 1989.

Like so many releases this year, “The American Spirit” was conceived well before Trump's election, but takes on new meaning because of it. McCullough, speaking in 2016 at the U.S. Capitol Historical Society, praises the immigrants who helped build the capitol. In a 1994 commencement address at Union College, he warns against the “purists” who shun the “empirical method.” At a conference in Providence, R.I., not long after the Sept. 11, 2001, attacks, he disputes assertions that “everything has changed.”

“But everything has not changed,” he said.

McCullough works hard on his speeches, spending days or more to find the right words for a graduation or occasion for national reflection, like his 2013 address in Dallas for the 50th anniversary of President Kennedy's assassination.

His talks have been mini-essays on the evolution of the presidency, the Declaration of Independence, his native Pittsburgh, the role of universities in public policy, or the lives of congressional leaders he thinks deserve more attention. An official at the U.S. Capitol Historical Society, Laura McCulty Stepp, said McCullough came to Washington a few weeks before his speech for research and to get a feel for the actual location.

In his address to the society, he lamented the “Dialing-for-Dollars reality” of the current Congress, but last year he had much harsher and more surprising words for the Republicans' presidential contender. In July, he and Ken Burns started the Facebook page Historians Against Trump.

Asked what he would tell Trump should he ever have the chance, McCullough said he would urge the president to study his predecessors. “He has to understand who has occupied that all-important role down through the years and what can be learned from their successes and failures, their conduct in the face of disappointment or in the face of seemingly overwhelming odds.”