Presidential security is very tight today and has its own special unit, but that wasn't always the case:
It wasn’t until 1902 that the Secret Service, created in 1865 to eradicate counterfeit currency, assumed official full-time responsibility for protecting the president. Before that, security for the president could be unbelievably lax. The most astounding example was the scant protection afforded Abraham Lincoln on the night he was assassinated. Only one man, an unreliable Washington cop named John Frederick Parker, was assigned to guard the president at Ford’s Theatre on April 14, 1865.
Today it’s hard to believe that a single policeman was Lincoln’s only protection, but 145 years ago the situation wasn’t that unusual. Lincoln was cavalier about his personal safety, despite the frequent threats he received and a near-miss attempt on his life in August 1864, as he rode a horse unescorted. He’d often take in a play or go to church without guards, and he hated being encumbered by the military escort assigned to him. Sometimes he walked alone at night between the White House and the War Department, a distance of about a quarter of a mile.