Olympic security has been a big concern since the Munich games of 1972, when members of a Palestinian extremist group killed eight Israeli athletes. Since then, the Olympics have largely gone off without major incidents, although one person was killed and dozens injured when a bomb went off at the Olympics in the U.S. city of Atlanta in 1996.
The Olympics are being held in Greece this year, and Mueller says he is troubled. Everything about this year's games is reported to be running behind schedule, from construction of stadiums to landscaping. Security is not an exception, despite the hundreds of millions of dollars being spent to protect the athletes and spectators.
Citing the Madrid bombings, which killed 190 people three days before the Spanish elections, Mueller says terrorists may "wish to influence events."
Mueller notes that government buildings, airports, and similar sites in the United States have been given unprecedented protection. He says he is concerned that terrorists may now shift their aim to places without adequate security -- so-called "soft targets."
Yet, there have been no terrorist attacks in the United States since the events of 11 September 2001, in which about 3,000 people were killed. And there is a very good reason for this, according to Christopher Prebble, director of foreign policy studies at the Cato Institute, a private policy research center in Washington.
"We've been on a constant state of alert since the morning of September 11, and that doesn't have anything to do with the Department of Homeland Security or the federal government or anything else. I think you go to a big gathering, and you're cognizant of the dangers," Prebble said.
Prebble says the U.S. government's security efforts also deserve credit for preventing attacks, but says those efforts have so far been enhanced by luck. He recalls a statement by the Irish Republican Army after a failed bomb attack in the U.K. in 1984: "Today, we were unlucky. But remember, we only have to be lucky once. You have to be lucky always."
There is also the concern, Prebble says, that the billions of dollars being spent to prevent attacks ultimately may not be as effective as the government believes. He says one word may best describe the money already spent.
"Misplaced. The fact is, that terrorists know to exploit weaknesses, and they rarely attack you where you're strong," Prebble said.
Kenneth Allard agrees that many important parts of America's infrastructure are not properly protected. Allard, a retired U.S. Army colonel who served as an intelligence officer in Europe, tells RFE/RL that America's ports, long-distance railroads, and commuter trains remain vulnerable.
But he says the Bush administration can still point to at least one major success.
"There are still some stunning gaps in our homeland defenses. That is going to be a work of many years. What we have done is we have managed to take the offensive in the field against the terrorists. And frankly, what it comes down to, is that those guys [terrorists] are busy running for their lives. That interferes with their ability to come after us," Allard said.
He cites the war in Afghanistan, which routed the Taliban and scattered the Al-Qaeda forces they harbored as the chief example of confronting terrorists. But he also points to the counterterrorism efforts of U.S. allies, including Pakistan.
Allard says he is more concerned about the continued potential for attacks in Europe, especially after what happened in Madrid. A Spanish court this week is due to question six more suspects in connection with the 11 March bombings. Reports say some 18 people have already been detained in connection with the attack. Most are from Morocco.