In a letter Tuesday, John McCain, Kelly Ayotte and Lindsey Graham pressed Obama on whether he sought help for U.S. personnel who were under attack. Ambassador Chris Stevens and three other Americans died in the Sept. 11 raid.
The three wrote that despite testimony from senior Obama administration officials and the chairman of the Joint Chiefs of Staff, a number of questions remain unanswered.
Graham has threatened to block Senate confirmation of the president's national security nominees over Libya. The letter makes no mention of that threat.