Given the threat posed by terrorists, it would be comforting if counterintelligence did not suffer the turf wars that seem to bedevil most presidential administrations. But the forced resignation of Director of National Intelligence Dennis C. Blair last week seems to stem not from his effectiveness, or lack of it, in keeping the homeland safe but from the fact that he alienated the White House and misconstrued his mandate.

Blair, a retired admiral, was the third intelligence director, a position created at the behest of the 9/11 Commission. The commission envisioned the director as the president's chief intelligence advisor and the official responsible for managing "the national intelligence program and oversee[ing] the agencies that contribute to it." In practice, that mandate shrank considerably. The director's chief responsibility these days is to coordinate intelligence-gathering.

Given that, one might think that Blair's dismissal was a reaction to the intelligence failures that allowed Umar Farouk Abdulmutallab, the alleged would-be Christmas Day bomber, to board a plane for the U.S. After all, Blair's departure follows a scathing report about "systemic failures across the intelligence community which contributed to the failure to identify the threat." But that report is hardest on the CIA and the National Counterterrorism Center, whose director is not being fired.

The causes of Blair's departure seem to be more mundane: conflict with CIA Director Leon E. Panetta over who would choose intelligence officials at U.S. embassies; the lack of a close, personal relationship with President Obama; and a grandiose notion of his position that reflected the 9/11 Commission's definition but not the more circumscribed role established by Congress.

It's questionable whether the position was necessary in the first place. But it exists, and at a minimum it has the responsibility for ensuring, as the saying goes, that dots are connected. It could acquire new importance if Obama follows the Senate Intelligence Committee's suggestion and entrusts the director with the task of reviewing the roles of counter-terrorism analysts throughout the intelligence community.

In replacing Blair, Obama should first and foremost decide on the contours of the position. Will the new director have operational responsibilities? If not, that should be made clear to Blair's successor, as should his role, if any, in personally briefing and advising the president. It may be that Blair's successor should concentrate on counter-terrorism, as opposed to the myriad other activities of the intelligence community. In any event, both the person and the mission should reflect the president's preferences. Otherwise, Blair's successor also will be marginalized.