Mr. Johnson wrote one on violating Pakistani sovereignty. When two countries are not at war, international law generally forbids one from using force on the other’s soil without consent. That appeared to require that the United States ask the Pakistani government to arrest Bin Laden itself or to authorize an American raid. But the administration feared that the Pakistani intelligence service might have sanctioned Bin Laden’s presence; if so, the reasoning went, asking for Pakistan’s help might enable his escape.

The lawyers decided that a unilateral military incursion would be lawful because of a disputed exception to sovereignty for situations in which a government is “unwilling or unable” to suppress a threat to others emanating from its soil.

Invoking this exception was a legal stretch, for two reasons. Many countries have not accepted its legitimacy. And there was no precedent for applying it to a situation in which the United States did not first ask Pakistan, which had helped with or granted consent for other counterterrorism operations. But given fears of a tip-off, the lawyers signed off on invoking the exception.

There was also a trump card. While the lawyers believed that Mr. Obama was bound to obey domestic law, they also believed he could decide to violate international law when authorizing a “covert” action, officials said.

If the SEALs got Bin Laden, the Obama administration would lift the secrecy and trumpet the accomplishment. But if it turned out that the founder and head of Al Qaeda was not there, some officials thought the SEALs might be able to slip back out, allowing the United States to pretend the raid never happened.

Image A staircase in the house where Osama bin Laden was killed.





Mr. Preston wrote a memo addressing when the administration had to alert congressional leaders under a statute governing covert actions. Given the circumstances, the lawyers decided that the administration would be legally justified in delaying notification until after the raid. But then they learned that the C.I.A. director, Leon E. Panetta, had already briefed several top lawmakers about Abbottabad without White House permission.