White House spokesman Jay Carney defended the strikes as legal under a 2001 law authorizing the use of military force against al-Qaida. CIA drones also have been used in attacks, including the 2011 killing in Yemen of U.S. citizen Anwar al-Awlaki, a cleric with suspected ties to at least three attacks planned or carried out on U.S. soil: the Fort Hood, Texas, shooting that claimed 13 lives in 2009, a failed attempt to down a Detroit-bound airliner the same year and a thwarted plot to bomb cargo planes in 2010.
But Congress has grown increasingly uneasy with at least some of the authorities. Democratic Rep. Barbara Lee of California, a staunch Obama supporter, calls the military force law "overly broad" and has been seeking to overturn it for years.
"He's got to end that," Lee said. She described a "huge difference in policies" between Obama and Bush but added: "I respectfully disagree on some, including the use of that (use of force) resolution, and that would not matter who was president. That resolution is there until we repeal it, and I want it repealed if we're going to end this state of perpetual war."
Lee is among the dovish Democrats who also are displeased with Obama's decisions to increase the number of U.S. troops in Afghanistan in 2009 and to lead NATO military airstrikes at the height of the Libyan crisis in 2011. But, in a testament to his case-by-case deliberations on foreign policy and national security, Obama refused to similarly intervene or arm rebels in Syria and opposes a near-term military strike on Iran. He also ended the U.S. war in Iraq by withdrawing all Americans troops by the end of 2011 as promised.
Still, Obama's hawkish counterterrorism bona fides are undeniable.
Determined to not bring any terrorist detainees to Guantanamo Bay, the government has begun interrogating suspects on Navy warships before they are given a chance to speak to a lawyer. The information from those interrogations, including in the case of al-Shabab operative Ahmed Abdulkadir Warsame, is not allowed to be used in court but it can be used to pursue others. And the FBI can later question the terror suspects. Al-Shabab is a Somali-based terrorist group that has been linked to al-Qaida.
The administration also has fought for, and won, the right to withhold evidence in terrorism lawsuits that it says could threaten U.S. security. The use of the so-called state secrets privilege gives the president limitless power to keep information from becoming public and hampers court oversight in cases that could be embarrassing to the government.
Critics say Obama's use of the state secrets privilege represents a surprising reversal by the constitutional lawyer-turned-president and threatens American civil liberties. Last month, a federal judge in New York chided the administration for refusing to turn over documents in a case relating to al-Alwaki's killing but said she had no authority to order them disclosed.
More than any other president in U.S. history, Obama has invoked the Espionage Act to prosecute government officials accused of leaking classified information to reporters. His administration has used the law six times in leak investigations since 2009 — compared with three since it was enacted in 1917.
"There has been a disturbing amount of continuity between this administration and the former one," said Elizabeth Goitein, co-director of the Brennan Center Justice's Liberty and National Security Program. The center is a civil liberties program at the New York University law school.
"There's been way more continuity than I think anyone expected, and certainly than candidate Obama had led anyone to expect," Goitein said. "I just think he put his tail between his legs — the national security establishment has become so huge and powerful that he's probably gotten somewhat co-opted despite himself and despite his better judgments and inclinations."
She noted that some of the most powerful players in Obama's national security circle were holdovers from Bush's administration, including Robert Gates, who served as defense secretary, FBI Director Robert S. Mueller and Brennan, who was a top CIA official until he retired in 2005.