US President Barack Obama is all set to achieve a major diplomatic victory on the Iran nuclear agreement when lawmakers return to Capitol Hill next week, a report says.

Democrats have enough votes to sustain the veto Obama has promised and now they are on the verge of filibustering the anti-Iran bill, preventing it from reaching the president’s desk for a veto, The Hill, a the Washington-based newspaper, reported on Saturday.

So far 38 senators - 36 Democrats and two liberal-leaning independents - have announced to vote in favor of the nuclear agreement in Congress, meaning Democrats will now have enough votes to protect it. They need 41 votes in the Senate to mount a filibuster.

At best, The Hill report said, opponents of the Vienna nuclear accord can only pass a measure of disapproval against the Iran nuclear deal.

Democratic lawmakers told the newspaper that the president is on the verge of gaining the most significant foreign policy achievement of his term because of weeks of tough lobbying, detailed technical arguments, grassroots support and even some help from Republican war hawks and Israeli Prime Minister Benjamin Netanyahu whose controversial address at Congress earlier this year turned the Iran nuclear issue into a partisan one.

“This was the most extensive effort by the administration on any single piece of legislation since I’ve been in Congress,” said Representative Adam Schiff, a Democrat from California.

“I think they were determined not to take support of the deal for granted and wanted to do everything possible to ensure the president’s veto was sustained,” he added.

President Obama, Secretary of State John Kerry, Energy Secretary Ernest Moniz and other high-ranking officials lobbied vigorously in favor of the agreement, answering every lawmaker’s questions in person before they fanned out across the country, the report said.

According to a White House official, Obama spoke to over 100 lawmakers in individual or small-group settings, and even made telephone calls during his two-week vacation last month in Martha’s Vineyard, Massachusetts.

And, Moniz offered a detailed yet affable performance on the Iran nuclear deal that contrasted with Kerry’s more pedantic style, which earned him the respect of even the agreement’s staunch opponents, The Hill reported.

In addition, cabinet secretaries and senior White House officials discussed the nuclear deal with more than 200 representatives and senators since July 14, when Iran and the P5+1 group of countries – the US, Britain, France, Russia, China, and Germany – announced the conclusion of nuclear negotiations in the Austrian capital, Vienna.

The Obama administration is set to gain this resounding victory over its opponents, despite the Israel lobby’s massive campaign to defeat the historic agreement in Congress.

The American-Israeli Public Affairs Committee (AIPAC) has deployed hundreds of lobbyists on the US Capitol to try to convince lawmakers to vote against the nuclear agreement.

According to reports, AIPAC and other pro-Israel lobbying groups have spent at least $40 million on television commercials and other propaganda material to inform the public “about the dangers of the proposed Iran deal.”