On the other side is the powerful American Israel Public Affairs Committee, which is spending millions of dollars on ads to convince lawmakers that Iran can’t be trusted and the deal should be scuttled.

Meanwhile, one of the most prominent Jewish Democrats in the House of Representatives, Sander Levin of Michigan, said that he is backing the Iran nuclear deal. “It’s a deal that takes no option away from a future president”.

US Secretary of Defense Ashton Carter acknowledged that the deal removes “a critical element of risk and uncertainty” in the region. “I think enough for this to be sustained”, Lew said on Wednesday.

Secretary of State John Kerry hit back against allegations that the deal would relax economic sanctions forever, in return for temporary concessions on the development of nuclear weapons.

Congress has begun a 60-day review of the worldwide agreement, with a vote expected in September.

Mr Obama has said he will veto any bill along those lines and Republicans will need a two-thirds majority in both houses to override his objections.

One House Democrat – Rep. Grace Meng of New York – came out against the agreement Wednesday, saying that “almost all of Iran’s nuclear infrastructure would remain intact”.

When a senator tried to characterize Dempsey’s support as “tepid”, the general corrected him; his support is “pragmatic”, he said.

Rep. Jerrold Nadler also noted that the US president “said you should vote based on your real conviction – not on politics”.

“He (Obama) asked for the meeting”. “He’s a very persuasive person and he knows his subject so I have to assume that if minds are open, some will be affected”.

David Albright, a former Iraq weapons inspector who now heads the Institute for Science and worldwide Security in Washington, said the demands for greater transparency aren’t unreasonable. “I reject a notion that the choice is simply between this deal and going to war“.

I followed the developments of these negotiations thoroughly and saw an Iran unwilling to make meaningful concessions.

Rep. Dan Lipinski, D-Illinois, hasn’t decided either.

“I have every confidence a better deal can be realized”, she added.

While Congress will be briefed on the contents of those agreements, “we respect the process of the IAEA and we don’t have the authorization to reveal what is a confidential agreement between them and another country”, Kerry told the committee.

“The immediate sanctions relief provided Iran in the deal would incentivize the funding of terrorism and lessen Iran’s interest in restraining its nuclear ambitions over the long term”, she warned.

At the often contentious hearing, Kerry sought to allay the concerns of McCain and other Republicans who repeatedly charged that they were being denied access to side agreements with the worldwide Atomic Energy Agency on verification measures in the proposed deal.

U.S. Secretary of State John Kerry testifies before a House Foreign Affairs Committee hearing on the Iran nuclear agreement in Washington, July 28, 2015.

Sen. Thom Tillis, R-N.C., said it was pointless to negotiate with Iran.

In an at times tense exchange, Kerry, Energy Secretary Ernest Monize, and Treasury Secretary Jacob Lew defended the deal between Iran and six nations aimed at preventing the Islamic Republic from building a nuclear weapon.