Sens. Chris Murphy (D-Conn.) and Patrick Leahy (D-Vt.) backed the Iran nuclear deal on Wednesday, becoming the latest Democrats in the upper chamber to endorse the agreement ahead of a five-week recess.
“The test for this agreement, then, is simple: is Iran less likely to obtain a nuclear weapon with this deal than without it?" Murphy said in a statement. "Because I answer this question affirmatively, I will support this agreement when it comes before the United States Senate for a vote in September."
Murphy, a member of the Foreign Relations Committee, had previously suggested that he was leaning toward supporting the agreement.
Leahy, meanwhile, suggested that without the deal Iran would be more likely to develop a nuclear weapon. He said rejecting the ageement would isolate the United States from the countries who participated in the diplomatic push.
"They stuck with us because we thought we were negotiating in good faith and we'd have a deal. If we walk out now, many of these countries are going to say, 'okay, you're in it by yourself,' " Leahy said.
"This is not a bad deal," he added.
The two endorsements come the day after Sens. Tim Kaine (D-Va.), Barbara Boxer (D-Calif.) and Bill Nelson (D-Fla.) also threw their support behind the deal.
Senate Republicans have largely lined up against the Iran pact, which means Obama will need the support of at least 34 Senate Democrats to uphold a potential veto of legislation disapproving of the agreement. Many Senate Democrats, including Minority Leader Harry Reid (D-Nev.), are still undecided.
Opponents of the deal are hoping to use the five-week break ahead of a vote to pressure roughly a dozen Senate Democrats to buck the president, but with more Democrats backing the deal before leaving town, it could be an uphill battle.
Republicans, including the party's presidential contenders, have taken issue with multiple parts of the agreement, including "side" deals between Iran and the IAEA, the lifting of an arms embargo and that it doesn't require Iran to recognize Israel or release Americans from custody.
Murphy sought to combat that criticism on Wednesday, saying that while the Iran nuclear agreement wouldn't impact other key U.S. criticisms of Iran, "America and our allies will still fight the Iranian regime tooth and nail on their support for terrorists, their constant threats to the U.S. and Israel, and their denial of political and human rights to their own people."
He also dismissed another key Republican criticism, that Congress could walk away from the agreement and press for a better deal, as "pure fantasy."
"This deal has many unsavory elements," he said. "[But] I understand that the nature of a negotiation by definition involves not getting everything you want. ... The agreement has flaws, but the prospect that a better deal would result from congressional rejection seems like pure fantasy to me."