An exterior view of the White House is seen October 2, 2003 in Washington, DC.Alex Wong
The world's tightest security surrounds the American president – rings of armour and glass and missile defences and motorcades and men willing to 'take a bullet' to protect him.
But Barack Obama lives in a massive White House in the middle of an American city and it's not tough to hit a building from a half a kilometer away. And it is easy to get within rifle range of the White House.
A shooter, firing an AK-47 – the ubiquitous Russian-made infantry weapon that can be easily bought at gun shops across America – apparently fired at least two shots at the White House last Friday. One smashed an outer decorative window before being stopped by an inner plate of armoured glass. The other bullet was found outside.
Soon after the shooting a car was found crashed near Theodore Roosevelt over the Potomac just west of the White House. Inside was a weapon and shell casings. Police identified a suspect.
On Wednesday, Oscar Ramiro Ortega-Hernandez, 21, was arrested at a hotel near Indiana, Pennsylvania.
The president was in California at the time of the Friday shooting. But even if he had been at home, the threat was minimal. The protection is layered to defend against a threat to the man, not the building. So, while there are surface-to-air missiles capable of shooting down an aircraft attempting to crash into the White House, it is both impossible and unnecessary to try and stop a bullet. Although the White House can been seen from many vantage points in Washington, presidential appearances – such as Rose Garden speeches and the walk to the helicopter – are out of sight and firing lines.
The road closest to the White House – Pennsylvania Avenue – has long been closed and turned into a pedestrian plaza. Most days it is full of strollers and tourists and a few protesters. There was a regular ball hockey game on weekends for a while. The Secret Service police, some in cars, some on bicycles, some inside the tall black fence wearing blast glasses and carrying machine guns, are evident.
Towards the Mall, the sprawling south lawn (where the choppers lands) provides a buffer. Beyond it the Ellipse and then Constitution Avenue from where – apparently – the two shots were fired.
Huge concrete bollards and movable columns that rise out of the road protect public buildings from truck bombs and random security checkpoints appear at periods of heightened alert.
What isn't publicly known is that both acoustic and radar devices capable of detecting incoming small arms fire, plotting trajectories and then calibrating the shooting point are almost certainly installed at the White House and other significant Washington sites including the Capitol.
But the reality is that it is no harder for a gunman to hit a building from a distance of several hundred metres in Washington than it would be to hit the Parliament Buildings in Ottawa. Except that in America, it is far easier to get a gun.