Romney then forgot his own talking points when he walked right into the Benghazi trap that Obama laid for him in the Presidential debate. Obama gave Romney two opportunities to withdraw the claim that he hadn't described the attack as terrorist then mowed his head off when Romney showed himself as to proud to admit a mistake.
Romney then further compounded the disaster by arguing with Cindy Crowley as moderator while she was trying to feed him the Republican talking point he was meant to be using.
Having attacked Clinton, Rice and Obama for 'lying' over Benghazi, the Republicans need to do rather more than show that their version of events could possibly be true. To substantiate their claims they would have to show that there is convincing evidence that the administration version of events is false and that it was known to be false when it was given.
In short, the GOP are demanding that their story be granted the very sort of allowance that they insist the administration version of events be denied.