Washington – Hours before President Obama makes a key speech to the nation to sell the Iran nuclear deal, Sen. Chris Murphy on Wednesday announced his support for it.

“Because as dangerous as Iran is today, it becomes twice as threatening to the security of the United States, Israel, and the world if its regional provocations were to occur under the cover of a nuclear weapons arsenal,” Murphy said in a statement.

The deal, which Congress will vote on in September, was negotiated by the United States, the other four permanent members of the United Nations Security Council, Germany and Iran. Under the deal, Iran would halt its nuclear program in return for a lifting of economic sanctions.

Murphy, the top Democrat on the Senate Foreign Relations Committee panel with authority over the Middle East, said, “A rejection would isolate the United States, since virtually all of our international partners support the deal and the United Nations Security Council has already approved it unanimously.”

“If we rejected the deal, it would be an ideal scenario for hardliners in Iran,” Murphy said. “American sanctions would remain, but the global sanctions regime would, at best, fray, and, at worst, fall apart. Iran would be able to resume its nuclear program, and our inspectors would be kicked out of the country, causing us to lose visibility of their potential progress toward a weapon.”

Murphy also said he realized the agreement was not ideal.

“This deal has many unsavory elements,” he said. “I would rather that its duration be longer. I would prefer our access to military sites to be less conditioned. I would like for Congress’s prerogative to impose additional non-nuclear sanctions on Iran to be clearer. But I accept that the perfect should not become the enemy of the good, and I understand that the nature of a negotiation by definition involves not getting everything you want.”

Sen. Richard Blumenthal, D-Conn., said he is undecided. Obama will try to sway undecided lawmakers and the public with a speech at American University Wednesday.

Republicans, nearly unanimously, have rejected the pact and are expected to propose a resolution of disapproval of the agreement in September. But there may be enough Senate Democrats who back the president to block the resolution in that chamber.