[Updated 3:30 p.m.] The closure of 19 embassies Sunday and the issuing of a month-long global travel alert for all Americans abroad shows how Al Qaeda's threat to the United States has evolved since 9/11 – and how the US response has evolved, too.
The closed embassies are all in an arc that runs from North Africa through the Middle East to Afghanistan, and the information suggests that the primary threat comes from Al Qaeda in the Arabian Peninsula (AQAP) – the Yemen-based Al Qaeda branch that many experts say is now the movement's strongest.
Officials with knowledge of the intelligence that led to the closures say the intercepts point to discussion of actual operations, not just typical chatter.
Some Obama administration critics have hailed the decision, with Rep. Peter King (R) of New York, who has been briefed on the threat, telling CNN: "I think the government is doing exactly the right thing here."
The closures are both a testament to Al Qaeda's persistent threat and perhaps also an indicator of how its aspirations have contracted since 9/11.
While Al Qaeda has by some measures become larger since 9/11, it has become less cohesive, according to a recent study by the RAND Corp., a defense and security consultancy. This means that the goals and capabilities of the various branches have shifted from attacking the American homeland to achieving narrower goals.
"They want to establish Islamic emirates in specific countries or regions, though they may be agnostic about a broader violent jihad," RAND terrorism expert Seth Jones said in congressional testimony last month.
One source interviewed by ABC News suggested that some American officials were worried about explosive devices surgically implanted into terrorists. AQAP, which launched the "underwear bomber" plot to destroy a plane on Christmas Day, 2009, is still trying to hit at the US aggressively.
But attacks on Western embassies in the Mideast would fit the broader profile of Al Qaeda's evolution.
In some ways, this is not unlike the pre-9/11 Al Qaeda. Before the attacks on New York and Washington, Al Qaeda's biggest strike was against the US Embassies in Kenya and Tanzania in 1998, which killed more than 200 people.
But post-9/11 political realities have reshaped America's response. Post-9/11 investigations faulted America's intelligence agencies for being fractured and failing to recognize telltale signs of an imminent attack. This year, the Obama administration is still facing congressional investigations looking into whether it failed to adequately secure the US Consulate in Benghazi, Libya, which was attacked on Sept. 11, 2012, killing four, including the US ambassador.
In explaining the embassy closures Thursday, State Department deputy spokeswoman Marie Harf told reporters the move was taken "out of an abundance of caution."
That could be the new watchword of US response to terror threats. In Boston, during the manhunt for the surviving Marathon bomber in April, police issued a "shelter in place" order for a half-dozen cities surrounding the spot where he was seen last – effectively shutting down a wide swath of the metro area for an entire day. Today, the Obama administration is taking a similar approach with the embassy closures and the month-long travel advisory.
"I think this, closing all of these embassies in the Middle East to North Africa, is in fact unprecedented. At least, I didn't see this during my career," Christopher Hill, a former US ambassador to Iraq, told CNN.
The warnings coincide with the end of the Muslim holy month of Ramadan this Wednesday, as well as a new message from Al Qaeda leader Ayman al-Zawahiri that called on followers to attack American interests.
While Representative King said the intelligence that led to the warnings was "the most specific I've seen," there were no specifics about targets. "We are focused on the Middle East, but it's a potential series of attacks that really could be almost anyplace."
Sen. Saxby Chambliss (R) of Georgia told NBC's "Meet the Press" that the chatter is "very reminiscent of what we saw pre-9/11." [Editor's note: The original version of the story incorrectly identified the program that hosted Senator Chambliss.]
The travel warning, which ends Aug. 31, states: "US citizens are reminded of the potential for terrorists to attack public transportation systems and other tourist infrastructure. Terrorists have targeted and attacked subway and rail systems, as well as aviation and maritime service."