In raising the US terror alert status during the holidays the White House is again facing one of the hardest issues of homeland security: how to provide proper warning without spreading needless fear.
Pegging the color-coded alert up at orange may have been overdue, say some experts. Even open communications from Islamic extremists have been hinting at increased activity for some time.
Last week Al Jazeera broadcast a statement attributed to Osama bin Laden's main deputy, Ayman al-Zawahiri, which threatened Americans "in their homeland."
But the US population as a whole should still not overreact. For the most part changes in alert level are meant as signals to police, border guards, and other professionals, says Randall Larsen, CEO of Homeland Security Associates in Washington.
"Unfortunately they are going to get a lot more overtime over the holidays," says Larsen. "For most of our average citizens this does not mean a lot."
The head of the Department of Homeland Security, Tom Ridge, announced the elevation of the nation's threat level at a press conference Sunday. Intelligence information indicates that terrorists may be once again seeking to use planes as weapons, said Mr. Ridge.
Other federal officials indicated that New York and Washington, plus unspecified West Coast cities, might be the terrorists' targets. They also indicated that aircraft originating overseas could be the most likely flights terrorists might try to use.
Americans should still go about their holiday business, but they should "be vigilant" and "have a good communications plan," said Ridge in a round of interviews Monday.
In the past, the Bush administration has been criticized for moving the terror alert color scale up and down too much. Between September 2002 and May of this year the White House called an orange alert four times.
The costs to state and local governments of increased security procedures are substantial - a total of upwards of $1 billion a week, according to David Heyman, director of Homeland Security Initiatives at the Center for Strategic and International Studies (CSIS).
The White House was running the risk that lower-level governments would simply begin to ignore the scale, as the state of Wyoming, among others, had threatened to do.
But the government seems to have become more conservative in its threat-calling, say some experts. The government also made an attempt to be more specific this time, with its reference to aircraft.
"This new warning reflects a real concern on behalf of the administration that the threat to Americans today is more serious than in the past," according to a written analysis by Mr. Heyman of CSIS.
It's difficult to find the balance between security and national convenience, adds Larsen of Homeland Security Associates.
One problem might be the lack of specificity in the alert system itself. Going from yellow to orange conveys a heightened sense of risk.
But how heightened? Where? Why? Hints from officials in news conferences can help, but they are far from definitive.
"Is it an increased threat of a couple car bombers in a shopping center, or a nuclear weapon in a major city?," asks Larsen. "How much do I need to worry?"
On Monday, at least, worry did not seem to be widespread in the nation. Interviews with shoppers and travelers indicated that the new alert level might not make much difference in many Americans' holiday plans. The fact that the alert level has been ratcheted up before, and nothing happened, was a typical sentiment.
"People have a lot on their minds. I'm not going to be deterred from shopping for my grandchildren," says Veronica Smith, of South Weymouth, Mass., who was out in Boston on Monday looking for gifts.
The presence of more overt security measures might change some minds over the next few days. Near the White House on Monday uniformed Secret Service personnel were stopping large trucks to be searched. In New York, National Guardsmen dressed in forest-green fatigues were patrolling Penn Station.
Elsewhere in New York, hundreds of extra police were patrolling other places considered possible targets, such as Wall Street, subway stations, and tourist attractions.
At some airports, including Seattle-Tacoma International Airport and Phoenix Sky Harbor, authorities were searching cars.
But many of those trying to get to holiday destinations simply accepted the security provisions as one more aspect of life in the post-9/11 age.
"It's a part of life," says Ranga Yera, a business passenger on an Amtrak train passing through New York. "We're much safer than a couple of years back ... there's more scrutiny of luggage and paperwork.
Those not from big cities that might be terror targets were even more sanguine.
"I don't pay attention," says Michele Sanger, an Amtrak passenger travelling for the holidays.
Sanger lives in Missoula, Mont.
"We're so remote we don't even see [the threat of terrorism] as a reality," she says.
America's role in the world was on the minds of a number of interviewees. To some, the US invasion of Afghanistan and Iraq has simply made the homeland a target. It will only encourage terrorists to try harder, in this view.
"Our actions in Iraq have inflamed anti-Americanism around the world and increased the chances for terrorism here," says Richard Harriman of Cambridge, Mass.
Others think that the US military actions will have the opposite effect, and stamp out terror around the world.
In a recent Monitor/TIPP poll a plurality of 49 percent of respondents thought US military efforts were putting the US ahead in the war on terror.
"It shows the terrorists that we won't put up with it," says Jeff Dowling, a stockbroker from Duxbury, Mass.
• Staff writers Noel Paul in Boston and Seth Stern in New York contributed to this report.