I feel like there's more than meets the eye here. In this polarized era, every Member of Congress voting together, even though the media, the CIA, former Attorneys General, foreign governments, and so many others. Basically everyone outside of Congress thinks it's a terrible thing. Members like Senator Corker explain all the reservations they have about the bill, but then they go and vote for it anyway!
If I had to guess I think this is intentionally a complete break of the USA with the Saudi government. Obama and the CIA and etc are giving the appearances of opposing it so afterwards Obama can still negotiate with Saudi Arabia if necessary, rather than the US face an immediate removal of diplomatic ties.
see I would think that, if it weren't for the fact that only 27 Senators voted for the amendment against the Saudi arms deal, with Lindsey Graham concern-trolling about the Saudis being essential bulwarks against spooky spooky shias.