President Barack Obama has failed to fulfill his repeated promises to end the “culture of secrecy” that has defined his administration’s use of drones to target Islamist extremists overseas, according to a damning report issued Tuesday by a leading Washington think tank.

The review by the Stimson Center, a nonpartisan research organization, gives the Obama administration an “F” for failing to provide a clear legal justification for its use of drones to kill al Qaeda or Islamic State extremists in countries where the United States is not at war. And the administration also receives an “F” for failing to ensure strong oversight and accountability for the secret program, which has become a signature of Obama’s tenure. There are also “Ds” and “unknowns” awarded to the White House on other aspects of the drone program.

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