It's kept us vigilant. But it's also become the political weapon of choice. We saw that during the Cold War, too. It was Sen. Arthur Vandenberg who created an enduring adage when he advised President Harry Truman to "scare the hell out of the country" to get his agenda through Congress. Some have come to believe that terror alerts and target lists have been used to stoke perhaps more fear than is necessary.
"Fear is essentially a political emotion, and a politically manipulated emotion at that," says Michael Ignatieff, director of the Carr Center at the John F. Kennedy School of Government at Harvard University.
Now: Police patrol a Metro car in August after a security alert.
(Sarah L. Voisin -- The Washington Post)
"So we have to be wary, as citizens, of any political leader who says 'Be afraid. Be very afraid. And vote for me and you'll be safe.' "
In the Cold War, the infamous "daisy ad" did this, with Lyndon Johnson suggesting a Barry Goldwater victory in 1964 would lead to a nuclear holocaust. Critics this week have slammed Vice President Cheney for doing it, when he warned that a vote for Sen. John Kerry could mean the United States will get hit by terrorists again.
"Politicians fall in love with a threat, because it makes their lives much simpler, so George W. Bush believes that his electoral fortunes will rise and fall over how well he can portray himself as a leader in the fight against terror," says David S. Meyer, professor of sociology and political science at the University of California at Irvine.
"The war on terror is the trump card that obviates all debate, and Kerry is doing the same thing," Meyer says, referring to Kerry's use of his military record.
One thing Meyer sees as a difference between the fear of the war on terror and that of the Cold War is that fear in the 1950s and 1960s became an organizing principle for a whole domestic agenda not directly related to security.
To stay strong in the test of wills with the Soviets, we had to look strong at home. We had to bulk up in education, especially the sciences. We had to soar into space. We had to get rid of those moral blots on our house, such as rampant racial discrimination.
The United States was "taking propaganda beatings in Europe," says Meyer, because of the continuing inequalities in a system that touted itself as free.
That, he says, was the upside of fear -- it helped propel an agenda for social change. (Meyer himself benefited, attending college on a national defense student loan intended to help the country compete with the Soviets.)
"Same deal with the war on terror," he says. "The war on terror gives people legitimate reason to build our public health infrastructure, to improve the care in emergency rooms across the country."
But fear, he cautioned, also can be used to justify what politicians might want to do anyway. The war on Iraq could fall into that category, since there were many in government whose desire to take out Saddam Hussein predated Sept. 11, 2001.
The impulse to focus on a single enemy, a nation, is straight out of the Cold War -- and wrong, says Stephen Flynn, a senior fellow at the Council on Foreign Relations and a military official in both the George H.W. Bush and Clinton administrations. The enemy is not a state. It's an ideology and a methodology. The United States hasn't figured out how to fight it, he says.
"The United States is living on borrowed time," he writes in a fear-inspiring opening line to his article in the journal Foreign Affairs.