(Reuters) - George H.W. Bush and his son George W. Bush did not vote for fellow Republican Donald Trump last year, says the author of a new book on the 41st and 43rd U.S. presidents in which they open up about their disapproval of the man now occupying the White House.

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The elder Bush voted for Hillary Clinton, while his son voted for neither Trump nor his Democratic challenger, or “none of the above,” said Mark K. Updegrove, who wrote “The Last Republicans” with the cooperation of the two Bushes. HarperCollins will publish the book on Nov. 14.

In an interview with the New York Times, Updegrove said the elder Bush, 93, who served as president from 1989 to 1993, had an instinctive dislike of Trump though he did not know him personally.

In an interview during the 2016 presidential campaign, George H.W. Bush told the author that Trump was a “blowhard,” driven by “a certain ego” and lacking a commitment to public service.

The younger Bush, 71, who served in the White House from 2001 to 2009, believed candidate Trump lacked both humility and a necessary understanding of the presidency, Updegrove said in previewing the book about the relationship between the Bushes, written with the cooperation of the father and son.

During the campaign, George W. Bush told the author that he feared he would turn out to be the last Republican elected president.

“At the time, I think he was concerned that Hillary Clinton would win,” Updegrove told the Times.

“But if you look at his values and those shared by his father and Ronald Reagan, they are very much in contrast to the values of the Republican Party today, in particular the platform that Donald Trump ran on, which is essentially protectionism and a certain xenophobia,” said Updegrove, a historian who has written several books about the presidency.

Updegrove could not be reached for further comment.

“The American people voted to elect an outsider who is capable of implementing real, positive, and needed change - instead of a lifelong politician beholden to special interests,” White House spokeswoman Sarah Sanders said in a statement.

“If they were interested in continuing decades of costly mistakes, another establishment politician more concerned with putting politics over people would have won.”

Like many Americans, George W. Bush was surprised that Trump fared so well in last year’s Republican state primaries, where his brother Jeb, a former Florida governor, emerged as one of Trump’s most frequent targets.

During the campaign, the billionaire real estate developer, a political novice, promised to “drain the swamp” in Washington, a vow that extended to the Republican establishment, which the Bush family epitomized.

The book follows a rare speech by the younger Bush in which he delivered a sweeping yet thinly veiled critique of the Trump administration’s policies and the president’s blunt style.

The 43rd president decried “bullying and prejudice” in public life while defending open immigration and trade, two of the pillars of previous Republican administrations that have come under sustained attack by the new president.