As it stands 41 Democrats have publicly backed the Iran deal. There has been a two month face of fierce campaigns with many Republicans and a few Democrats opposing the deal. The number is enough for President Obama to stop the Republicans effort to stop the deal in Senate. Obama will not need to exercise a veto especially if all the backers support a filibuster.
The pro-Israel lobby group called American Israel Public Affairs Committee has spent a lot of money on ads and also included face-to-face pressure in Capital Hill. However they lost by a far margin. A progressive pro-Israel group called J. Street and the National Iranian American Council had also led similar efforts as well. However, the Democratic Party didn’t use so much financial firepower to organize campaigns that would support the deal.
In July Obama lamented “What we have to rely on are grassroots networks and me being able to get on the horn with a bunch of rabbis and hopefully they’re paying attention.” Things are turning out to be quite effective. As of Tuesday morning the Democrats were still three votes short of the required 41 and before noon three other Senators had declared their support.