Senators Chris Coons and Bob Casey become the 32nd and 33rd Democrats in the Senate to announce support for Iran nuclear deal.

President Barack Obama is closer to being able to uphold a veto of a Republican resolution against the Iranian nuclear deal, after two more Democratic Senators announced Tuesday they would vote in favor of the deal.

The two Senators are Chris Coons (D-DE) and Bob Casey (D-PA), who become the 32nd and 33rd Democrats in the Senate to announce support for the deal. Obama now needs only one more Democrat to reach the 34 votes needed to uphold a veto of the Republican-drafted resolution against the deal.

Coons's decision, disclosed in an exclusive interview with The Washington Post, delivered a powerful blow to opponents of the plan because the Delaware Democrat had previously voiced some of the deepest skepticism about the controversial deal.

The interview came as Casey announced support for the deal as well, the newspaper reported.

Coons reached his decision after many weeks of deliberation that included long talks with top administration officials, including Vice President Biden, and an exchange of letters with President Obama that codified the assurances he received about the pact's implementation.

"We are better off trying diplomacy first," Coons told The Washington Post. He will formally announce his position Tuesday afternoon at the University of Delaware, during which he is expected to explain the administration's position that this deal would give the United States a stronger long-term position over Iran because of the international backing it has.

"They are saying what I need to hear," he said of Biden and other Obama officials.

Casey voiced similar sentiment, saying, according to The Post, "This agreement will substantially constrain the Iranian nuclear program or its duration, and compared with all realistic alternatives, it is the best option available to us at this time.”

With Coons joining their ranks Tuesday, Obama's allies in the Senate have shifted their game plan from winning the 34 Democrats needed to uphold the presidential veto, to also pushing for the support of 41 Senate Democrats so that the resolution would die in a filibuster.

In his interview with The Washington Post, Coons said that this was one of the most difficult votes of his five-year tenure in the Senate, but not because of the AIPAC-led media campaign. Instead, Coons said, he has made calls and held face-to-face conversations with many friends and longtime political supporters who have strongly held beliefs against the deal.

Ultimately, Coons told the newspaper was convinced that this deal offered the best chance of keeping a strong international hand on Iran.

Casey voiced similar views that, if the deal is implemented well, it will leave the U.S. military in a stronger place to take action if the Tehran regime violates its tenets. "I believe this agreement must be undergirded by a clear and unequivocal statement from both the Administration and the Congress: we are prepared to take military action if Iran attempts to develop a nuclear weapon," said Casey, who like Coons, is a member of the Senate Foreign Relations Committee.

So far, only two Senate Democrats — New York's Chuck Schumer and New Jersey's Bob Menendez — have announced that they will vote against the deal, which Congress has until September 17 to approve or reject.

Menendez, who chairs the Foreign Relations Committee and is a leading voice against the deal, acknowledged last week that the White House lobbying campaign for the Iran nuclear deal has generated results, and said he doesn't know if opponents of the deal can prevail.

Earlier on Tuesday, Iranian Foreign Minister Mohammad Javad Zarif expressed his hope that Congress will not be swayed by what he termed the "propaganda" of "warmongers".

"We believe it's a mutually beneficial agreement," Zarif said of the July 14 accord on reining in Iran's controversial nuclear program in exchange for a lifting of international sanctions.

"And if people are not too much concerned with the propaganda being raged by warmongers in our region and outside our region, there's no reason for the deal to face any impediments in the United States," he added.