Welcome back to an earlier era: namely, the terror twilight between the Kenya and Tanzania embassy bombings of 1998 and 9/11. To boil down the best sources of information about this period -- Steve Coll's Ghost Wars, the 9/11 Commission Report, and the latter chapters of Richard Clarke's Against All Enemies -- the situation facing the Clinton and Bush administrations was roughly the following:

There's a metastasizing threat from al-Qaeda centered around Afghanistan. Judging from al-Qaeda's past actions and statements of intent, it will murder increasing numbers of Americans if allowed. The surest way of eliminating the threat is to invade Afghanistan and destroy al-Qaeda's bases of operations. But that option would never receive domestic or international support absent the very attack that you seek to prevent. U.S. covert action, whether through direct CIA or Special Forces operations or a reliance on local proxies, are all suboptimal, carrying with them the risks of outright mission failure, intolerable levels of civilian casualties, driving the Afghan population closer into the hands of al-Qaeda, or some combination of the above. What to do?

Clarke's answer, after the Cole bombing, was a multifaceted strategy that accepted the covert-action component. George Bush felt frustrated that the strategy amounted to "swatting at flies," and wished for something more robust. As a result, nothing significant in terms of strategy occurred before 9/11, which allowed for the more-robust option of invasion to become available. (At the cost of 3,000 lives.)

Five and a half years and two wars later, here we are again. In today's Times, U.S. intelligence officials raise the concern that al-Qaeda's core pre-9/11 leadership has achieved sufficient sanctuary in Pakistan's Waziristan province as to reassert a level of control over its disparate allies, confederates and franchisees. Whether this is a correct inference to draw is, of course, unclear. The publicly-available evidence for it centers around the increased volume of communications from "Core al-Qaeda" -- bin Laden and Zawahiri, basically -- and amorphous connections between last summer's would-be London airline bombers and Pakistan-based al-Qaeda operatives.

But to a degree, whether or not al-Qaeda Prime is reasserting central command and control is besides the point. What's clear is that al-Qaeda Prime has a level of sanctuary in Pakistan that allows it to do more than what we want it to do -- that is, run or, preferably, die. In a recent paper for the Jamestown Foundation, Chris Quillen, a former CIA terrorism analyst, intriguingly speculated that this sanctuary may in fact be sufficiently desirable to al-Qaeda Prime as to form the basis for deterring it from a chem-bio-radiological-nuclear attack. (That is, to do so would disrupt a balance of terror between the U.S., Pakistan and al-Qaeda and risk an unacceptable loss of the sanctuary through a U.S./Pakistan/joint invasion or assault.) Its efficacy as an organization from a remote location shouldn't be doubted.

All of this isn't to suggest that some qualitative change in al-Qaeda Prime's position has recently occurred. It's to underscore the larger strategic fact that after the invasion of Afghanistan, we find ourselves in a comparable situation to the unhappy 1998-2001 era. Invading Pakistan isn't politically tenable, nor, quite possibly, militarily sustainable beyond a few months. Indeed, Pakistan has opted to return to its pre-9/11 strategy of brokering truces with tribal leaders in Waziristan instead of harassing them militarily. If anything is to be done, it's to be done with a flyswatter -- something likely to remain obscured if al-Qaeda Prime pulls off another attack and an American political consensus demands an invasion of, say, Syria or Iran in its anger.