Isaac Herzog, right, the leader of the Zionist Union party in Israel. He is expected to visit U.S. politicians in an effort to lobby against the Iran nuclear deal. (Anna Loshkin/European Pressphoto Agency)

Jewish American organizations are lining up on opposing sides of the Iran nuclear deal, arming themselves for multimillion-dollar campaigns targeting lawmakers still undecided about the agreement.

The opponents’ campaigns will be bolstered by visits to the United States by prominent Israeli politicians, including Isaac Herzog, the leader of the Zionist Union opposition, who has said he would work with Prime Minister Benjamin Netanyahu to stop the “dangerous” agreement.

The backers of the agreement are getting help directly from the White House. On Thursday, deputy national security adviser Benjamin J. Rhodes met at the White House with Jewish Democratic members of the House to address concerns and rally support.

The American Israel Public Affairs Committee is funding a new 501(c)4 group, Citizens for a Nuclear Free Iran, that is expected to spend $20 million to $40 million on advertising and campaigns in 30 to 40 states to mobilize opponents of the deal to write or call their members of Congress, say people familiar with the plan who sought anonymity because they were not authorized to discuss it.

On Friday, a spokesman for Citizens for a Nuclear Free Iran, Patrick Dorton, a partner at the communications firm Rational 360, said the group would get money from other organizations and individuals, too, and would highlight “the dangers of the proposed Iran deal.” The group has hired Democratic political veterans Mark S. Mellman, Mark Putnam and Trilogy Interactive. (Dorton would not comment on the size of the group’s budget.)

Iran has finally reached a nuclear deal with the U.S. and international partners. Here's what's in the deal, and what happens next. (Gillian Brockell and Julio C. Negron/The Washington Post)

The Republican Jewish Coalition, which also opposes the deal, is targeting 24 senators and twice as many House members seen as being on the fence. It will try to get its 40,000 members to write to lawmakers who are Jewish or who have large numbers of Jewish constituents and to attend town hall meetings held during the congressional recess.

“I think it’s going to be a really epic fight. The foreign policy fight of a generation,” said Jeremy Ben-Ami, president of J Street, a liberal advocacy group. “It pits folks who brought us the Iraq war and whole neocon worldview versus the Obama worldview and the concept that we can confront enemies with diplomacy.”

J Street, which backs the Iran nuclear agreement, is mobilizing supporters in its own $2 million to $3 million effort. It has already produced a digital ad comparing the Iran deal to the accord President Ronald Reagan reached with the Soviet Union, about which Reagan said “trust but verify.”

“We don’t need to trust Iran to honor a nuclear agreement,” the ad says. “This deal mandates the toughest inspection program in history.”

Ben-Ami said the outcome of the battle is not certain. Congress has 60 days to review the agreement and can vote to reject it, but it would require a veto-proof majority, or two-thirds of both houses of Congress. Ben-Ami notes that a letter supporting the president’s diplomatic efforts in the spring gathered signatures from 146 voting members in the House, one more than needed to sustain a presidential veto.

Among the main targets of lobbying groups are Sen. Charles E. Schumer (D-N.Y.), who enjoys the support of Jewish constituents and respect among other lawmakers. “Call Senator Schumer,” says the home page of the American Security Initiative, whose board includes former senators Joseph I. Lieberman (I-Conn.), Evan Bayh (D-Ind.), Norman Coleman (R-Minn.) and Saxby Chambliss (R-Ga.).

“This is a bad deal for America, a bad deal for Iran’s neighbors in the Middle East and a bad deal for the world,” Lieberman told House Foreign Affairs Committee members this week. “This is a bet based on hope over experience that we’ve had with Iran.”

What's next for Iran after the nuclear deal

“He’s a very important vote. And I think some people will look to him,” said Victor A. Kovner, co-chair of J Street’s political action committee and a partner at the law firm Davis Wright Tremaine. Kovner, a longtime supporter of Schumer, said “people know his commitment to Israel, and that will lend weight to his comment and analysis.”

Other key lawmakers include Sens. Benjamin L. Cardin (D-Md.) and Christopher A. Coons (D-Del.) and Reps. Steny H. Hoyer (D-Md.), Eliot L. Engel (D-N.Y.) and Brad Sherman (D-Calif.).

“The president has the luxury of not being held accountable on the deal, at least not at the ballot box,” Josh Block, president of the Israel Project, said. “But if you’re in the House or Senate, you’re going to be directly accountable for this.”

Block said that now that there is an actual agreement, many lawmakers will reconsider their position and that the text of the agreement provides material to use to attack the deal. For example, the agreement lifts economic sanctions on a long list of Iranian individuals and companies, including, Block said, Qasem Soleimani. An Iranian major general by that name commands the Quds Force of the Revolutionary Guard Corps and has trained Iraqi Shiite forces to fight American and allied soldiers in Iraq.

“If you’re a member of Congress, do you want someone to campaign against you saying here’s the man General David Petraeus called evil, and we’ve just given him billions of dollars?” Block said.

But as if to demonstrate the complexity of the negotiations, Undersecretary of State Wendy R. Sherman on Thursday said there are two men named Qasem Soleimani. One was the head of a uranium mining company, and sanctions will be lifted on him first. The other, head of the Quds Force, would come off the U.N. sanctions list in phase two of the agreement “some years away.” She said the administration would leave him on the U.S. sanctions list.

The White House has also said that the agreement has enough safeguards to make sure that Iran does not stray from the accord and attempt to build a nuclear weapon. Those safeguards include visits by inspectors, electronic surveillance and monitoring all along the nuclear weapon supply and development chain.

But the detailed and technical nature of the debate might make public opinion subject to ads summarizing or characterizing the accord.

“Can you get people down into the weeds on this thing?” Block asked. “The administration hopes not.”

President Obama has argued just the opposite: The details of the agreement provide reassurance that safeguards are as strong as they can be.

The White House had a list ready Tuesday, the day the agreement was announced, of benchmark concerns issued while talks were still underway by the Washington Institute for Near East Policy and explanations of how the agreement met each of those tests, including possible military dimensions in the past, monitoring and verification, limits on advanced centrifuges, sanctions relief and consequences of violations.

Abe Foxman, national director of the Anti-Defamation League, said his organization was not campaigning on the agreement.

“Having read it, we’re not for it — but we can be convinced,” he said. “We will submit a series of questions to lawmakers encouraging them to probe and ask and get answers.”

Foxman said that “at this point we’re opposed. There are too many risks, too many unanswered questions. Too much that will, at end of the day, be determined by the Iranians.”

Foxman said that unlike many critics of the deal, he doesn’t question Obama’s motivation. But he took issue with Obama’s framing the agreement as a choice between this deal or war.

“Does that mean those of us who don’t want this are warmongers?” he said. “I think that’s unfair.”