One lesson from this week's sabotage of a passenger train in the Arizona desert is sobering: It shows how vulnerable US infrastructure can be to attack.
While security experts say that railroads, with their endless ribbons of remote track and low traffic volume, are a particularly easy target, no part of the nation's transportation, power, and communications network is exempt from possible sabotage.
The derailment in Arizona is already spurring a reassessment of security at the nation's railroads - and may force other institutions to relook at their safety plans.
Robert Kupperman, a senior analyst at the Center for Strategic and International Studies (CSIS) in Washington, says the attack's implications for the safety of the nation's infrastructure are ''dismal.''
Not only are railroads vulnerable, he says, but so are airplanes, highways, communication systems, and electrical power systems.
''There are plenty of other targets,'' he says. ''If you knock out two key transformers, you can knock many miles of electrical grid off line for months.''
Stephen Gale, a professor at the University of Pennsylvania who studies terrorism, says transportation systems are particularly vulnerable. There are many place to hit and disrupt them - from bombings to tinkering with electronic systems to hijackings. ''Of all the parts of the American infrastructure, [transportation] is, by definition, the most wide open,'' he says. ''It's supposed to be easily accessible, that's the whole point.''
Yet Harvey Burstein, a former FBI agent who now teaches at Northeastern University in Boston, says railroads are unusually easy to sabotage.
In order to attack an airport, he notes, a terrorist has to be ''within hailing distance'' of the building, and all the police and cameras and security scanners there. Highways are harder to disable, too, he says, because they are patrolled by police, have a high traffic volume and frequency, and are plied by drivers with phones and radios.
By contrast, he says, one stretch of railroad track could go unused for hours at a time, and it would be ''impossible to police every mile of track in the US.''
In Arizona, the culprits, with little more than a crowbar, a spool of wire, and 10 minutes of darkness, managed to create a catastrophe that killed one crew member and lured a caravan of television trucks to the desert.
According to materials found at the site, an unknown group called the ''Sons of the Gestapo'' took credit for the sabotage. If this is true, it would be the second such attack by right-wing, antigovernment groups this year, and a signal that domestic terrorism may be on the rise.
That the attack may have been politically motivated causes some security experts to question the way American institutions have reacted to terrorist threats.
WHILE Mr. Burstein says federal agencies should be questioned when they make mistakes, he notes that Congress has spent weeks dissecting the role of federal agents in the raid at the Branch Davidian Compound in Waco, Texas, and the siege and shootout at Randy Weaver's cabin in Ruby Ridge, Idaho, but has spent less than one full day conducting hearing on the right-wing militia movement.
This blurring of priorities, Burstein says, has created an atmosphere where such dramatic terrorist attacks produce widespread ripple effects in Washington.
He says the FBI's $3 million payment to Randy Weaver for the deaths of his wife and son in the Idaho shootout could encourage some terrorists to try to extort money from the government.
According to Mr. Gale, the advances in the size and speed of media coverage also act as a spur to political terrorism. ''Terrorists know they can use the media like an amplifier for whatever cause they support,'' he says. ''The media offers the grand possibility of getting on television worldwide. Why doesn't the fourth estate play these acts down? Because they need product.''