There’s no way they are going to get 67 votes to reject so Flake has the ok to pass on this one to shore up his “opposition” cred.
Normally these kind of things are called treaties and require a 2/3 majority to pass.
Obama knew he couldn’t get there so he had the Uniparty led by Corker pass legislation that stands the Constitution on its head and requires 2/3 majority to reject this so-called Iran “deal”.
Still more to go to get there.