A top secret letter sent to the Senate Select Committee on Intelligence in 2011 boils down the rationale for the expansion of government surveillance since 2001 and, perhaps, contains clues as to why so many US embassies are shut across the world this week.

Anonymous US government officials told reporters that "intercepted messages" and "chatter" among Al Qaeda members imply that electronic surveillance of the kind conducted by the National Security Agency (NSA) was involved in raising the alarm. Since Sept. 11, 2001, both the Bush and Obama administrations have made improving this kind of intelligence collection a priority, and for a good political reason: the US public's alarm that another 9/11 could happen again and its demand that the government do everything to prevent it.

While a popular conspiracy theory that has emerged on the Internet the past few days, particular among people opposed to NSA surveillance, has held that the embassy closures are an elaborate ruse to scare US voters into acquiescing to US intelligence practices, the letter that was declassified at the end of last month spells out the position of successive governments.

The letter from Assistant Attorney General Ronald Weich, prompted by a request for information about the legality of NSA intelligence collection efforts, seeks to justify use of secret warrants issued under the Foreign Intelligence Surveillance Act (FISA) courts by saying that 9/11 could have averted. It reads in part:

Prior to the attacks of 9/11, the NSA intercepted and transcribed seven calls from hijacker Khalid al-Mihdhar to a facility associated with an al Qa'ida safehouse in Yemen. However, NSA's access point overseas did not provide the technical data indicating the location from where al-Mihdhar was calling. Lacking the originating phone number, NSA analysts concluded that al-Mihdhar was overseas. In fact, al-Mihdhar was calling from San Diego, California. According to the 9/11 Commission Report (pages 269-272): "Investigations or interrogation of them [Khalid al-Mihdhar etc], and investigation of their travel and financial activities could have yielded evidence of connections to other participants in the 9/11 plot. The simple fact of their detention could have derailed the plan. In any case, the opportunity did not arise." Today, under FISA Court authorization pursuant to the "business records" authority of the FISA ... the government has developed a program to close the gap that allowed al-Mihdhar to plot undetected within the United States while communicating with a known terrorist overseas. This and similar programs operated pursuant to FISA, including exercise of pen/trap authorities, provide valuable intelligence information.

The closures of 20 US embassies and consulates across the Middle East and Africa, the largest since 50 were shut for a week after 9/11, is a reminder of American voters' and politicians' intolerance for risk in missions abroad, something that was driven home by the partisan shouting about the Obama Administration's failure to protect its massive CIA operation operating under the cover of the consulate in Benghazi, Libya, last September.

Susan Rice, Obama's current national security adviser and ambassador to the United Nations at the time of the Benghazi attack, came under withering attack and months of posturing by members of Congress followed alleging a coverup. The aftermath of the tragic deaths of Libya Ambassador Chris Stevens and three other Americans in Benghazi made the domestic political costs of failing to take hints and warnings of danger with maximum seriousness abundantly clear.

But more broadly, amid the drive-time talk-radio fury that the closures are signs of American "weakness" under Obama, the decision also speaks to how US intelligence collection has changed – and how it's used – since Sept. 11, 2001 and, perhaps, since the Aug. 7, 1998, Al Qaeda bombings of the US embassies in Tanzania and Kenya, which killed more than 200 people, 12 of them American citizens. This Wednesday is the 15th anniversary of that attack, which led to overhaul of diplomatic security globally. In the past, Al Qaeda and its allies have used the anniversary of the Africa attacks as inspiration to strike again.

What is really going on? The US government says intelligence indicated a large-scale attack was being planned for US interests abroad, but it clearly doesn't know the exact details, since the likelihood of coordinated attacks in 17 countries is precisely zero. Has an attack been diverted or delayed? We simply don't know – though I'm disinclined to believe the popular Internet conspiracy theory that this is all being down by the US government to scare the public into supporting National Security Agency (NSA) surveillance.

But is it possible that patterns are being seen in signals intelligence collection that aren't really there? Or that the worst possible spin is being put on what is being heard by analysts and political appointees trained by experience to err on the side of caution? Yes.

The sales pitch made for an expanded NSA effort for years has boiled down to: These new laws and methods help us prevent another 9/11, which has since been America's overriding national security concern and prompted the creation of the Department of Homeland Security and its $40 billion-plus annual budget. And while the attacks are alleged to have been planned for foreign targets abroad, the Obama administration's unnamed spokesmen have been putting out that the "intelligence chatter" is similar to what was picked up, and not acted upon, ahead of Sept. 11, 2001.

Are the embassy closures an overreaction? This is the frustrating part of it. Maybe they are, maybe they aren't. It's impossible to make a reasonable assessment of the Obama administration's decision without more information. And while the US government clearly overclassifies information, keeping some things secret on the most tenuous of national security grounds, other secrets are reasonable and appropriate. Which is it this time? We don't yet know.

But another frustration is how that partisan hay is once more being made, with allegations that the closures are a sign of Obama's "weakness," since the implication is that if he was "stronger," Al-Qaeda-style groups wouldn't dare plot attacks against US interests. (In my experience, it's very hard to frighten militants who are willing to carry out suicide bombings, no matter how much "strength" you project.)

Typical of the partisanship over this were former Sen. Jim DeMint's comments on Fox News over the weekend. Mr. DeMint, who now runs the conservative Heritage Foundation, said that "it's clear that Al Qaeda may be more of a threat to us than they were before 9/11 now" and "the instability around the world is clearly related to at least a perception of a lack of resolve of the United States and a perception of weakness."

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In the past 12 years the US has, in a bipartisan fashion, increased intelligence collection, moved away from protecting the privacy of individuals in favor of greater collective security, engaged in its two longest foreign wars in the name of fighting Islamist terrorism, and made "security first" the unofficial logo of missions abroad. It has, of course, failed to completely destroy the small number of people inspired to carry out attacks against US interests because they view America as implacably hostile to their own goals.

But making the whole world love the US is a difficult if not impossible task. We will do well to think on the compromises we've made in the name of security this week, as we watch and hope that feared attacks don't materialize.