Already on high alert since September 11th, much of the US ratcheted up security yet again at the weekend as TV channels warned repeatedly of the "near certainty" of retaliatory attacks on home soil.
Federal buildings, military and nuclear facilities, ports, airports, bus and train stations, road tunnels and even sports stadiums stepped up checks and searches, and some state capitol buildings closed to the public.
In the White House, President Bush yesterday morning swore in to his Cabinet his head of the new Office of Homeland Security, Governor Tom Ridge of Pennsylvania.
Mr Ridge, a former senator and a decorated Vietnam veteran, is a close friend an ally of the Bush family. He will be based in an office in the West Wing, with a staff of 100.
A Homeland Security Council consisting of Mr Bush, the Vice-President, Mr Dick Cheney, Mr Ridge and various agency heads will tackle domestic terrorism much as the National Security Council advises the President on international affairs.
Mr Bush paid tribute to Mr Ridge's experience and has given him the authority to co-ordinate and review the work and budgets of some 40 federal agencies which have in the past often failed to communicate with each other.
Mr Ridge said he was determined to close such gaps and promised both to listen to critics and to eliminate turf wars.
"Everyone in the homeland must play a part ... The difficult we do immediately, the impossible may take a little longer," he promised.
In Detroit on Sunday, Metro Airport spokeswoman Ms Barbara Hogan said the Federal Aviation Administration notified officials at 2 p.m. to put additional security in place.
It all will be "behind the scenes" and not noticed by passengers, she said.
Several airport representatives said they were increasing the number of visible, armed personnel.
The Coastguard was conducting the largest port defence operation since the second World War, designating 72 special zones of security around specific potential targets.
All cruise ships have been banned from New York harbour.
In New York and Washington rail stations passengers on intercity trains were being asked for ID cards and on-train ticketing was ended.
Drivers entering Manhattan through tunnels faced car searches.
In New York, Mayor Rudolph Giuliani said more security checkpoints manned by armed police and the National Guard were set up on Sunday.
But he vowed no bridges, tunnels or public places would be closed unless there was a specific threat.
Yesterday's Columbus Day parade went ahead as planned.
"We have to go about our normal way of life," he said.
The State Department on Sunday issued a worldwide caution to Americans, warning of the possibility of "strong anti-American sentiment and retaliatory actions against US citizens and interests throughout the world."
It asked governments to increase their security on US embassies.
The government spirited Vice-President Dick Cheney to an undisclosed location.
Military bases went on a war footing, with the Nebraska Warren Airforce Base, where 200 nuclear missiles are stored, ordered to the highest "Force Protection Charlie" status, in expectation of and readiness for an imminent terrorist attack.
The Energy Department alerted nuclear plants, labs and storage depots to increase their security.
Administration officials have also been meeting secretly with managers of the nation's water system and haulage companies.
Officials of the Department of Health and Human Resources have taken steps to secure stockpiles of drugs and vaccines.
Armed guards have been posted to protect such installations as the BioPort company in Lansing, Michigan, which is producing anthrax vaccines, and the Center for Disease Control in Atlanta.
