"I believe that Israel, the region, and the world are far more secure if Iran does not move toward possession of a nuclear weapon. I believe the Agreement is the best way to achieve that," said Democratic Rep. Sandy Levin in a statement.
The support of a veteran Jewish representative, who has served Michigan for 33 years, could be significant in building momentum for Democratic backing of the deal. Several of the senior Jewish members of Congress, including New York Sen. Chuck Schumer, poised to become the next Democratic leader in the Senate, have not yet disclosed where they stand on the deal.
Some of the most vocal opposition to the nuclear agreement has come from the Jewish community and pro-Israel constituents, who are concerned that the deal would endanger Israel. The Israeli government has harshly criticized the agreement and warned it will lead to Iran obtaining a nuclear bomb, an assertion the White House has strongly disputed.
Levin's statement comes amidst an intense debate on Capitol Hill over whether to vote down the deal. Congress is in the midst of a 60-day review period, and Republicans have widely indicated their opposition. As long as Obama can maintain support from members of his own party, he will have enough votes to sustain his veto of a congressional challenge.
But it's still an open question whether he can do that. There have been key Democratic voices supporting the deal, including House Minority Leader Nancy Pelosi and Senate Intelligence Committee ranking Democrat Dianne Feinstein, both of California. But others have voiced criticism, including Sen. Bob Menendez of New Jersey, until recently the Senate Foreign Relations Committee ranking member, and Rep. Eliot Engel of New York, ranking member of the House Foreign Affairs Committee.
President Barack Obama will get a chance to convince some wavering Democrats to back the deal before they head home for a month-long summer break, when opponents will ramp up efforts to block it. The president invited all House Democrats to the White House for a "working reception" on Wednesday night.
But Engel detailed his concerns with the deal to CNN Tuesday. The agreement, which phases out after 15 years, "only postpones Iran from having a bomb and that's my major concern," he said.
In a House Foreign Affairs Committee hearing Tuesday, Kerry warned that should Congress vote down the deal, it would collapse entirely because the U.S. wouldn't be able to provide the sanctions relief that Iran is due to receive in return for curbs on its enrichment of uranium, reductions in the number of its centrifuges, submission to intensive inspections and other requirements.
"To those who are thinking about opposing this deal because of what might happen in year 15 or year 20, I ask you to simply focus on this: If you walk away, year 15 or 20 starts tomorrow and without any of the long-term access and verification safeguards we have put in place," he warned.
Kerry will return to the Hill Wednesday in another part of their own campaign to win support, and Engel suggested they were likely to be successful in their appeals to fellow Democrats.
The lawmaker said the expectation is that Congress would initially vote to reject the deal and that Obama would veto that. Engel said he is unsure if the two-thirds of lawmakers necessary to override a veto would support the bill after that.
"I don't think it's impossible, but I think it's a very difficult thing to accomplish," he said.
Engel, like Menendez and Schumer, represent districts with many Jewish voters. Schumer in particular has been subject to an intensive lobbying campaign by outside groups to oppose the Iran deal.
As incoming Senate minority leader, Schumer will have an outsize role in determining whether the White House gets the Democratic votes it needs. While Schumer isn't looking to break with his party's president on something key to his legacy, he's also has his constituents to answer to.
Arizona Sen. John McCain, a Republican critic of the deal, pointed to the difficult position Schumer is in while speaking to reporters Sunday.
"Glad I'm not Chuck Schumer, I tell you," he said. "Boy he's got the toughest vote of his career coming up, as you know."
Schumer himself has declined to show his hand on whether he supports the deal.
Last week he told CNN that he's still considering the matter. "It's a serious issue and I'm studying it carefully and giving it what it deserves," he said following a classified briefing on the agreement. "You know, lots of things are in the agreement but lots of things you need to hear what people say or how it is interpreted, other facts and bits you need to know to see how the agreement works."
Other leading Democrats have also refraining from taking a public stand at this point.
No. 2 House Democrat Steny Hoyer, still undecided on the deal, said Tuesday that he will meet with top Israeli officials next month to discuss the agreement. The 60-day review period ends in mid-September.
"There are a lot of very heavy consequences of a vote for or against," the Maryland congressman said. "I've urged members to take as much time as they have available to them to be as confident as they can make themselves that their vote is the right vote for their country, for stability in the Middle East."
Hoyer is traveling to Israel in early August with other House Democrats to discuss Israeli Prime Minister Netanyahu's "very deep concerns" with the Iran deal.
Debbie Wasserman Schultz, a Florida representative and the chairwoman of the Democratic National Committee, told CNN Monday that she needed more time to decide.
"My constituents at home have very strong opinions. It's a very well-educated pro-Israel district and, you know, I have a lot of respect from them and their opinion and I want to seek it while also making sure that I thoroughly understand all its implications," she said. "And as a pro-Israel legislator myself, it's very, very important to get this right."
Though some members of the American Jewish community have been among those pushing Congress most strongly to vote down the deal -- a charge led by the American Israel Public Affairs Committee -- Jewish voters express a diversity of views.
A survey of 501 American Jews conducted by the Los Angeles-based Jewish Journal in mid-July found that 53% think Congress should approve the deal versus 35 percent who think it should be opposed. There was a 6% margin of error.
However, the general public's attitude about the deal is more negative. A CNN poll released
Tuesday found that 52% of Americans think Congress should reject the deal, while 44% say it should be approved. The survey of 1,017 adults was conducted last week and has a 3% margin of error.
Republican presidential candidates have been particularly harsh critics of the deal.
Several 2016 GOP candidates took to Twitter during Kerry's appearance on Capitol Hill to assail the agreement.
Former Pennsylvania Sen. Rick Santorum called on followers to retweet him "if you agree Barack Obama's #Iran deal is the worst national security blunder in our history #StandWithIsrael."
And Texas Sen. Ted Cruz tweeted that the agreement would make the White House an abettor of Iran's bad behavior: "If #IranDeal goes through, Obama Admin will become the world's leading financier of radical Islamic terrorism."