Just how much face would the US lose if the President were to announce "It is clear that nothing is clear. Due to the lack of compelling, direct, unequivocal evidence and the severe collateral risk which would result from military action, we deem such action at this time to be inappropriate and call for all parties to arrange peace talks at a neutral location."
Rather a lot, I would contend, given what has already been said. If the statement made some conciliatory remark about reflecting the national and international mood, not wanting to inflame an already delicate situation, whilst making it clear that the use and proliferation of all categories of WMD is condoned and will not be tolerated by the international community, and re-affirming the role and importance of the UN to act in such instances, then he might just get away with it.