DOVER — Congress is set to vote on the historic Iran deal within the next month, and all three members of Delaware’s congressional delegation remain undecided, at least publicly.

A group of world powers, including the United States, met with Iran in March and April to negotiate an agreement that would prohibit Iran from obtaining a nuclear weapon in exchange for the lifting of economic sanctions. Exact terms were reached, and the Joint Comprehensive Plan of Action was signed on July 14.

Delaware’s two senators and one congressman, all of whom are Democrats, are still making up their minds, according to representatives for them reached this week.

Sen. Chris Coons, D-Del.

Sen. Chris Coons has been the most hesitant member of Delaware’s congressional delegation in regard to the proposal.

“The agreement must include strict limits on advanced centrifuge research and development to prevent a rapid upgrade of Iran’s future capacity to enrich uranium,” he said in a July statement. “Any sanctions relief must be based on Iran first meeting its obligations under this deal. Finally, the international community must maintain its ability to re-impose sanctions should Iran violate the agreement.”

Since the announcement, Republicans in Congress have criticized fiercely the plan, which is also opposed by Israel. Democrats generally have been supportive of President Barack Obama, with a few exceptions.

Congress has a 60-day review period, meaning lawmakers have time to consider the deal before they vote on it. While the House of Representatives and the Senate can reject the deal, the president can issue a veto.

Sixty-seven votes are needed in the Senate and 290 in the House to overturn the veto. While it is possible every single Republican votes against the resolution, that would still leave the majority caucuses needing a number of Democrats.

Thirteen Senate and 44 House Democrats would be needed to override the president’s veto.

Many media outlets have noted Sen. Coons is a potential “no” vote. So far, just two Democratic senators have publicly announced their opposition, including New York’s Sen. Chuck Schumer.

In a statement, Sean Coit, a spokesman for Sen. Coons, said the senator has “significant concerns” and remains undecided.

Sen. Coons has heard from the White House, with President Obama and Vice President Joe Biden urging him to vote in favor the proposal, according to media reports.

He’s also been targeted by interest groups opposed to the agreement.

The American Security Initiative, an organization led by a bipartisan group of four former senators that is “dedicated to promoting legislation and urging Americans to stand up for the importance of a strong national security and foreign policy,” has created an advertisement focused on Sen. Coons. The ad urges Delawareans to call in and express their opposition.

Sen. Coons has been a strong supporter of Israel, and influential pro-Israel groups like the American Israel Public Affairs Committee are against the agreement with Iran.

Outside organizations also have called for Democrats to back the president.

Sen. Tom Carper, D-Del.

Like Sen. Coons, Delaware’s senior lawmaker, Sen. Tom Carper, also officially is undecided. However, he is leaning in a different direction than his counterpart.

“Sen. Carper is inclined to support the deal, but he’s using his time in August to review the text before making his final decision,” spokeswoman Katie Wilson said.

A spokesman for Rep. John Carney provided a statement issued by the representative last month.

“I’m pleased to hear that an agreement has been reached — I look forward to studying the details of it with skeptical and clear eyes. The central question is whether we are indeed better off with the deal than without it,” Rep. Carney said.

Rep. John C. Carney Jr.

“As I’ve said all along, a good deal must curtail Iran’s pursuit of a nuclear weapons program and put in place a tough regime of inspections that will ensure that Iran is playing by the rules. International inspectors need complete access to Iran’s known nuclear facilities and to other secret facilities that might be used to get around the terms of the agreement.

“I look forward to classified briefings on the specifics of the deal so that I can better assess its merits. I will continue to work with my colleagues in Congress to determine whether this agreement is, in fact, in the best interest of the U.S. and our allies in the region, especially Israel.”