President Barack Obama’s “most persistent distraction” when he launched his re-election campaign in April 2011 was not the economy, the Tea Party movement, the GOP presidential primary field, the unpopularity of Obamacare, or even the soon-to-be-launched mission to take out Osama bin laden.

No, the most pressing issue for the president was the fact that real estate mogul Donald Trump had been challenging him over his birth certificate, according to the new book Double Down: Game Change 2012.

“[T]he most persistent distraction Obama was facing personified by Donald Trump, the real estate billionaire and reality show ringmaster who was flirting with making a presidential run under the banner of birtherism—the crackpot conspiracy theory claiming that Obama was born in Kenya and thus was constitutionally ineligible to preside as commander in chief,” authors Mark Halperin and John Heilemann note in the opening chapter of the book.

While Obama—who was born in Hawaii—thought of the theory as “lunacy” and “simply mental,” in 2008 his campaign posted his short-form birth certificate online. But as 2011 rolled around, the theory, the authors note, “wouldn’t go away.”

“A recent New York Times poll had found that 45 percent of Republicans and 25 percent of voters overall believed he was foreign born,” Halperin and Heilemann wrote. “And with Trump serving as a human bullhorn, the faux controversy had escaped the confines of Fox News and conservative talk radio, reverberating in the mainstream media.”

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