Today marks eight years since the horrific attacks of 9/11. Most law enforcement officials will tell you the country's security has improved after the attacks. Al Qaeda has been degraded and many of its leaders have been killed.
But on matters of terrorism, there is always a caveat. U.S. pressure has forced al Qaeda into a more decentralized organization in which its major leaders, such as Osama bin Laden and Ayman Zawahiri, probably are not directing specific attacks.
Still, the group retains enough people and infrastructure to remain "lethal," officials said. And U.S. intelligence officials also worry about groups and individuals around the world who are inspired by al Qaeda, even if they don't report directly to its leadership.
There are indications this worry may be very well-founded.
In a July interview with ABC News, Attorney General Eric Holder said he was troubled by the emerging threat.
"The whole notion of radicalization is something that didn't loom as large a few months ago ... as it does now," Holder said. "And that's the shifting nature of threats that ... keeps you up at night."
What was Holder talking about? Here are some specifics:
This summer, a 26-year-old Long Island, N.Y., man was charged with attacking U.S. soldiers in Afghanistan and providing al Qaeda with details about the New York transit system. Investigators suspect he was radicalized in the United States and overseas.
Then, in sleepy Caswell County, N.C., seven men, most of them in their 20s, were accused of training to become terrorists. The FBI said the men were recruited to fight overseas by 39-year-old Daniel Patrick Boyd, who fought in Afghanistan against the Soviets in the late 80s.
In June, an Arkansas man and recent Muslim convert was charged with killing a U.S. Army recruiter in Little Rock, Ark., a day after viewing radical Islamic videos. The suspect is believed to have traveled in Yemen.
The FBI is conducting a massive investigation to find out who convinced 20 young Minneapolis men of Somali descent to fight in a civil war in Somalia.
FBI officials said it proves that there still are radicalized recruits out there who might be convinced to attack the United States at home. If such people cannot be found and neutralized before they attack, there are a host of "soft targets" in a democratic, free society that remain vulnerable, such as hotels or malls.
Here are some reflections about where things stand from homeland security, law enforcement, intelligence officials and other experts. Issues of chemical and port security and interoperability of different security systems top the list of concerns and gaps that some experts cite.
"The kind of vulnerabilities that were revealed to us on 9/11 clearly persist," said Stephen Flynn, senior fellow for counterterrorism and national security studies at the Council on Foreign Relations. "We still have a heavy concentration of chemical facilities near large population centers working with potentially very deadly substances. ... The risk of exposure of people potentially downwind is enormous."