These are historical facts:
Senate passes Iran sanctions 100-0; Obama objects (really) - The Washington Post
400-25 vote sends Iran bill to president
So 2/3 is actually very easy for them. Israel has to just go around and do some lobbying, and there is a good possibility that the vote might turn to become unanimous. 100%. It has happened before on Iran related matters (see links above).
But if Obama does some arm twisting then maybe the American representatives will stop to represent Israel for a day.
Either way, it is good for Iran. If it is stamped ok by congress, the deal is going to benefit Iran. If congress cancels the deal, then all the blame will be on US and the whole world will blame US. Not only that, but also Iran will most probably ratchet up its nuclear program to heights unimaginable. Also in future no body in the world will take US president and US secretary of state seriously anymore as they will be seen inconsequential and their agreements and words worthless.
It is win-win for Iran.
Obama will have to lobby for Iran left and right convincing people. And this is the coolest part of this show.