Since Obama took office, the rate of threats against the president has increased 400 per cent from the 3,000 a year or so under President George W Bush, according to Ronald Kessler, author of In the President's Secret Service.
According to The Telegraph, some of the threats issued against Obama, whose Secret Service codename is Renegade, have been publicized.
They include 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 of the threats have, however, been 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 Obama's inauguration in Jan 2009, 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 scrutinized.
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 mingle with them in order to get close enough to shoot the new president.
After Obama was elected president, his two children Malia, codenamed Radiance, and Sasha, codenamed Rosebud, began receiving Secret Service protection.
Obama's wife Michelle is codenamed Renaissance. The Secret Service also started to protect Vice-President Joe Biden's children, grandchildren, and mother.
Instead of bringing in more agents - instantly identifiable because of their bulky suits, worn over bullet-proof jackets, and earpieces - the Secret Service directed agents to work longer hours to cover the extra load and to miss firearms training, physical fitness sessions and tests.
"We have half the number of agents we need, but requests for more agents have fallen on deaf ears at headquarters," a Secret Service agent told Kessler.
The Secret Service has increasingly cut corners after it was absorbed by the new Homeland Security Department under Bush.