EXCLUSIVE – The author of an extensive biography on Barack Obama said a series of missteps both at home and abroad made his presidency a failure, and a key strategic error concerning Donald Trump could have helped his rival's political rise.

David Garrow, the author of the lengthy 2017 biography "Rising Star" that chronicled Obama's formative years and past relationships before he was married, said Obama today bore "astonishingly little resemblance" to who he was in 2000, when he was known as a hustling Illinois state senator who even had an urge to work across the aisle. 

"I think he began to change… He was a wonderful legislator," Garrow told Fox News Digital. "He's very actively reaching out to conservative Republicans to work with them. He's taken the job real seriously. Some of the other Black state senators are making fun of him for being, you know, a sort of nerd who's not Black enough. But after the congressional loss, his need to prove himself and his incredibly surprising success in that Senate primary and in early 2004, that begins to change him up."

Obama's decision to challenge Rep. Bobby Rush for his U.S. House district's Democratic nomination in 2000 surprised onlookers at the time. Rush enjoyed strong connections with his district's Black residents and high name recognition, in contrast to Obama, who was relatively unknown and lived in what the New York Times called the district's "rarefied neighborhood" of Hyde Park. Obama's elite education and connections to the White liberal establishment were used against him, and he later admitted he knew halfway through the campaign he was going to lose.

Biden and Obama

WASHINGTON, DC - SEPTEMBER 07: (L-R) Former U.S. President Barack Obama and U.S. President Joe Biden arrive at a ceremony to unveil the official Obama White House portraits at the White House on September 7, 2022 in Washington, DC. ((Photo by Kevin Dietsch/Getty Images))

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Rush beat him in a landslide, but Obama picked up the pieces and mounted a successful bid for the Illinois U.S. Senate nomination for 2004, and his career's meteoric rise didn't stop until he'd served two terms in the White House. 

But once he was in national office, the bipartisan Illinois figure was gone, Garrow says, calling one of his worst attributes his "failure to interact with congressional Republicans with the seriousness and social ease that he manifested back in Springfield."

"I mean, in the late '90s, he knew how to work successfully with Republicans more conservative than Mitch McConnell," he said. "Yet by the time he becomes president, is unwilling to engage with congressional Republicans. Barack, as president, was vastly more partisan than the Barack in Springfield had been 20 years previously. That's a really important point."

He added one of Obama's signature accomplishments in office –  the Affordable Care Act health reform law better known as Obamacare – was a mere gift to insurance companies and not the landmark achievement liberals want to celebrate. Garrow did laud Obama as a "superb" presidential figure in office and his family as an "ideal" one for the country to embrace, but he said he mostly erred abroad.

"I think that the most critical aspects of the Obama presidency are in foreign policy, and that is being increasingly viewed as a legacy of failure in not objecting more forcefully to the Russian takeover of Crimea and then the Eastern Donbas in 2014, and then the failure to go into Syria after you say that using chemical weapons against civilians is going to be a red line, and the Syrian regime uses the weapons and Barack backs off?" Garrow said. 

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FILE: Oct. 4, 2013, President Obama during an interview with The Associated Press in the White House library in Washington, D.C.

FILE: Oct. 4, 2013, President Obama during an interview with The Associated Press in the White House library in Washington, D.C. (AP)

"I think it's also fair to say that the intervention in Libya, as well-intentioned as it was, is virtually unanimously viewed as a failure," he added. "And then, there's no question that for all its other faults, the Trump administration did a vastly better job in acknowledging and confronting the challenge that the Chinese Communist Party poses in an ongoing basis and that the Obama administration did not, in a timely fashion, appreciate the scale or the danger of the Chinese Communist challenge."

Obama famously remarked in 2016 that he did not believe Donald Trump would be elected president, but like so many others, he was proven wrong when the billionaire political rebel defeated Hillary Clinton that November. Obama welcomed Trump to the Oval Office for the transition and attended his inauguration, but privately he fumed. According to top aide Ben Rhodes, he called Trump a "cartoon" and questioned whether he'd underestimated the same country that had sent him to the White House.

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Garrow said one of Obama's gravest errors may have been allowing the "birther" conspiracy theory to take root by not taking it more seriously from the outset. While it was in the air in 2008 when he first ran for president, the issue took off even more in 2011 when Trump, then best-known as an NBC television personality, made headlines with his continued claims that Obama wasn't a natural-born citizen and thus ineligible for office. The White House eventually released the "long form" birth certificate that showed Obama was born in Hawaii on Aug. 4, 1961.

Former president Barack Obama (2nd R) and President Donald Trump share a laugh as former First Lady Michelle Obama (R) and Melania Trump look on following inauguration ceremonies swearing in Trump as the 45th president of the United States on the West front of the U.S. Capitol in Washington, U.S., January 20, 2017. REUTERS/Mike Segar - RTSWJBX

Former president Barack Obama (2nd R) and then-President Donald Trump share a laugh as former First Lady Michelle Obama (R) and Melania Trump look on following inauguration ceremonies swearing in Trump as the 45th president of the United States on the West front of the U.S. Capitol in Washington, U.S., January 20, 2017. REUTERS/Mike Segar - RTSWJBX (Reuters)

Obama even roasted him about the conspiracy theory at the White House Correspondents Dinner that year, with Trump in the audience and looking none too pleased at those and other jokes that evening at his expense. Trump sat out the 2012 contest against Obama but took the plunge in 2016 and began his astonishing surge to the presidency.

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"One mistake that the Obama White House made was in not taking the birther claims with the political seriousness that they should have," Garrow said. They let that grow and grow, and that contributed to Trump's rise. If they had put out the long form birth certificate way earlier and realized that while, this was crazy, it also needed to be taken down, they could have taken a lot of air out of Trump way earlier than they did."

Fox News' Brian Flood contributed to this report.

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