Some threats to Mr Obama, whose Secret Service codename is Renegade, have been publicised, including an alleged plot by white supremacists in Tennessee late last year to rob a gun store, shoot 88 black people, decapitate another 14 and then assassinate the first black president in American history.
Most however, are kept under wraps because the Secret Service fears that revealing details of them would only increase the number of copycat attempts. Although most threats are not credible, each one has to be investigated meticulously.
According to the book, intelligence officials received information that people associated with the Somalia-based Islamist group al-Shabaab might try to disrupt Mr Obama's inauguration in January, when the Secret Service co-ordinated at least 40,000 agents and officers from some 94 police, military and security agencies.
More than a dozen counter-sniper teams were stationed along the inauguration parade route and the criminal records of employees and hotel guests in nearby buildings were scrutinised.
Despite all this, there were glaring loopholes in the security. Kessler describes how more than 100 VIPs and major campaign donors were screened by metal detectors but then walked along a public pavement before boarding "secure" buses and were not checked again.
It could have been relatively simple for an assassin to have mingled with them in order to get close enough to shoot the new president.