Rep. Debbie Wasserman Schultz (D-Fla.). (Lynne Sladky/AP)

Democratic National Committee Chair Debbie Wasserman Schultz said Sunday that she will vote for the nuclear agreement with Iran, ending speculation about whether a top party leader would support President Obama, who had tough time corralling the votes to preserve the controversial deal.

Wasserman Schultz, whose Florida congressional district is heavily Jewish, faced intense lobbying on both sides and said during an interview Sunday on CNN's "State of the Union" that her decision-making process was "gut-wrenching."

"I concluded that the best thing to do is to vote in support of the Iran deal and make sure that we can put Iran years away from being a threshold nuclear state, and ensure that we can more closely concentrate on their terrorist activity," she said. "So I will be casting my vote to support the deal and, if necessary, to sustain" a presidential veto of any legislative effort by congressional opponents to dismantle the deal.

[Obama secures votes to protect Iran nuclear deal]

Obama won his struggle to secure enough votes in the Senate to fend off a veto Wednesday when Sen. Barbara A. Mikulski (D-Md.) became the 34th senator to pledge support for the agreement to curb Iran's nuclear development program.

Congress is expected to vote on the deal as early as this week. The accord, reached in July between Iran and the United States, Russia, China, Britain, France and Germany, calls for Iran to reduce its enriched-uranium stockpiles, mothball centrifuges and agree to inspections and monitoring in exchange for the gradual lifting of sanctions.

Some prominent Democrats, including Sen. Charles Schumer (D-N.Y.), have said they will not support the deal. Wasserman Schultz was blamed for scuttling a resolution put forth at the DNC's summer meeting late last month in Minneapolis that would have offered backing for the nuclear agreement with Iran.

[Dems say party chair blocked Iran resolution at DNC meeting]

Wasserman Schultz said she was and remains concerned about some aspects of the deal. "I worry that the vigilance over the life of the deal may wane, not the United States' vigilance, but, you know, with the IAEA's enforcement, with the world that has been a party to this, that complacency could set in. I worry that the additional resources, no matter how little, that Iran would get access to, that they could divert to terrorist activity would cause harm to Jews and others around the world," she said.

But, she said, she concluded that there wasn't a better alternative, including "opponents' claims that we could using our banking system, for example, to wrestle our allies and Iran back to the negotiating table for a so-called better deal, no one presented me with any evidence to show me that that was possible."

The party chairman's voice cracked at one point during Sunday's interview when host Jake Tapper asked her what she would say to "Jews who are going to say, you sold out Israel."

"I’m the first Jewish woman to represent Florida in Congress. I'm a Jewish mother," she said. "There's nothing more important to me, as a Jew, to ensure that Israel's existence is there throughout our generations. And I'm confident that the process I have gone through to reach this decision is one that will ensure that Israel will be there forever. It's the homeland of my people."

"I'm an American citizen, and I believe fervently in protecting America's national security interests. And there's no way that we would be able to ensure that better than approving this deal and ensuring that Iran is not ever able to get access to nuclear weapons, and that we can shift our focus with the rest of the world on going after their terrorist ambitions," she said.

Wasserman Schultz also said that Obama had agreed to make her part of a group of lawmakers that will work on an enhanced security plan for Israel.

Here's what's in the Iran nuclear deal, and what happens next. (Gillian Brockell and Julio C. Negron/The Washington Post)