But under Updegrove's analysis of their values and those of past Republican presidents compared to Trump's exhibition of Republicanism, the title still stands. And if you talk to those around him, they have confidence in his leadership.
"And that begins with the Iraq war, one of the greatest foreign policy mistakes in American history", the official said.
Last month George W Bush gave a speech in NY that appeared to be a sweeping, yet thinly veiled critique of the Trump administration, its policies, and the President's blunt style.
Trump repeatedly blasted the second Bush administration's decision to invade Iraq during the 2016 primaries, as he was running against George W.'s younger brother, and George H.W.'s son, Jeb. Meanwhile, the younger Bush told him during the general election that no matter who won, he feared he would be the last Republican president.
The book's author, Mark Updegrove, interviewed the Bushes past year - long before Trump's inauguration - and found neither wanted to see what they described as a coarse, populist campaigner become president. I don't know much about him, but I know he's a blowhard. He also noted that Trump lacks humility.
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"When Trump started to rise, I think he became concerned because he saw this populism of Donald Trump getting in the way of America's position in the world", Updegrove said.
"This guy doesn't know what it means to be president", he said.
This is not the first time that the younger Bush has criticised the United States president.
The 93-year-old reveals he voted for Mrs Clinton at the 2016 election and describes Mr Trump as a "blowhard" driven by ego, who lacks a commitment to public service.
A White House official told CNN, in response to the Bushes' comments, "If one presidential candidate can disassemble a political party, it speaks volumes about how strong a legacy its past two presidents really had".
In a speech on October 19, W. Bush took aim at bullying from public figures while Trump was embroiled in a feud with a Democratic congresswoman over whether he made an insensitive remark to the grieving wife of a fallen soldier.