The Grand Ayatollah Khamenei has signalled his support and there was celebration in the streets as thousands honk horns and screamed in relief...most Iranians are young, quite enamoured with things Western/ American and were born after the 1979 Revolution and they were the ones who voted for the moderate Pres. Rouhani. They want peace and they want to travel. They have suffered under the sanctions and they want it to end.
It was the sanctions that forced Iran to the table. That is because it was universally supported. Iran may have pursued the building of nuclear weapons but after the search for WMD and the subsequent war on and defeat and death of Saddam, they were became very concerned lest they be the next target and so limited their programme and allowed for inspection.
The terms agreed upon will see a severe limit on what Iran can do. There is a 10-15 years reduction of the amount of uranium produced and have in hand; there is a reduction of 2/3 of its 2,700 uranium-refining centrifuges; tough international monitoring, with IAEA, able to inspect suspicious sites....intense scrutiny and verification, so that it may well be impossible for Iran to secretly get a nuclear weapon.
Netanyahu's contention that Iran cannot be trusted and that they will continue to develop and build is pure sabre-rattling and has little or no credibility, but he says this to rally his neo-conservative friends in America and his hardliners at home. The idea that Iran will launch an attack on Israel is laughable, as Iran would face obliteration from Israel's arsenal of nuclear weapons.
If the Congress succeed in stopping the agreement ( they will face a veto and the over-ride requiring 2/3 of the Senate is not likely), here is what will happen. Russia and China will no longer support the UN sanctions. Not even France, the UK, the EU or Germany will support it. So Iran will be able to sell its oil and will be able to trade with the world, except US and Israel, and there will a rush to get the weapons to defend itself in case of an attack by Israel ( which Obama will not support). There 80 millions Iranians waiting to buy all manner of products which the world is ready to sell.
Deals that could have been worked out to fight ISIL; to end the civil war in Syria and Yemen; to apply pressure to Hizbollah, the Taliban and the Houthis will not be made. The region will be further locked in instability and wars, secular, regional and religious
Diplomacy and multilateralism will have failed and the drums of war will be everywhere. The world would be a far worse place without the agreement..