People have aimed trucks, helicopters and planes at the White House, but never until Saturday had anyone simply fired a modern firearm at America's most heavily guarded building.
Now agencies responsible for presidential safety are once again reviewing White House security that has protected presidents and their families from injury _ up to now. One question being asked is whether the Secret Service can continue to allow tourists and others to stroll freely on the sidewalk in front of the White House.
The White House is an enticing target of powerful symbolism for the disgruntled, unbalanced and dissenting. There have been intruders, but those who scaled the 10-foot-high wrought-iron fence have been quickly captured.
Only last month, a stolen single-engine Cessna light aircraft crashed onto the White House lawn a few yards from the president's Oval Office. The pilot, who reportedly had a history of alcohol and drug abuse, was killed in the crash.
That incident stirred a vigorous debate about whether White House security was lax. Secret Service officials acknowledged that if a man with limited flying skills could come close to hitting the president's bedroom without resistance, a trained assassin could inflict even greater damage.
They have acknowledged, however, that there is little that could be done to counter an assault on the building. Their strategy would instead be defensive: to move the first family and others to a safe place within the compound, the basement for instance, rather than risk their lives or the lives of those outside by firing back.
Shortly after the incident, security officials said a series of steps had been taken to enhance the protection of the president, though for security reasons they would not disclose them. The officials also announced they would review security measures around the White House. The review is still under way.
The White House always has sharpshooters and lookouts on the roof of the building when the Clintons are in residence. It was not clear if the lookouts spotted the gunman Saturday before he started shooting.
In addition, bomb-sniffing dogs check every vehicle and all visitors and staff go through metal detectors while cameras cover the lawns. And the Secret Service has never denied speculation that some rooftop guards have Stinger anti-aircraft missiles.
"You walk a fine balance here," White House chief of Staff Leon Panetta said Saturday of security policies.
"You try to . . . provide the greatest security possible for the president of the United States. But at the same time you want to provide access for people of this country to the White House."
Three presidents have been assassinated _ Abraham Lincoln (1865), William McKinley (1901) and John Kennedy (1963) _ but no president has been hurt within the White House.
Here are some of the main events disrupting White House security:
1828: Drunken crowds broke furniture in the White House while celebrating the inauguration of President Andrew Jackson, who was unhurt.
1938: The present metal fence atop a low stone wall was erected. Until then people had been free to enter the grounds.
1950: Puerto Rican separatists attacked Blair House, across Pennsylvania Avenue from the White House, in an attempt on the life of President Truman, who was unhurt.
1974: Army Pvt. Robert Preston, 20, hijacked a helicopter from Fort Meade, Md., and landed it on the South Lawn. Guards fired shotguns at the helicopter. Preston was apprehended.
1976: A man tried to ram a pickup truck through the White House gate but failed.
1983: Three-foot-high concrete flower pots barricades were erected around the perimeter of the White House and security was generally stepped up.
Sept. 12, 1994: Frank Corder crashed a plane at the White House lawn, killing himself.