A leading Republican senator said Sunday he would hold up Senate confirmation of President Barack Obama’s nominees to head the Defense Department and the CIA until the White House provided more answers about the deadly Sept. 11 attack against a U.S. installation in Benghazi, Libya.

The White House took aim at Sen. Lindsey Graham, a persistent critic of Obama’s response to the terrorist assault, by urging quick approval of the president’s second-term national security team and scolding any lawmakers trying to “play politics” with critical nominations.

Graham accused the White House of “stonewalling” requests to release more information about the attack that killed four Americans, including the U.S. ambassador to Libya. “We’re going to get to the bottom of Benghazi,” he told CBS.

A Democratic colleague branded Graham’s threat to stall the nominations of former Sen. Chuck Hagel to be defense secretary and John Brennan, Obama’s top counterterrorism adviser, to be CIA director as “unprecedented and unwarranted.” Senators should have the chance to vote on the fate of those nominees, said Sen. Jack Reed.