Maryland Sen. Barbara Mikulski became the 34th Democrat to come out in favor of the nuclear agreement with Iran on Wednesday, September 2, handing Democrats the number of votes they need to keep the deal alive in Congress despite Republican attempts to dismantle it, CBS News reports.

"I have concluded that this Joint Comprehensive Plan of Action is the best option available to block Iran from having a nuclear bomb,” Mikulski declared in a statement. “For these reasons, I will vote in favor of this deal. However, Congress must also reaffirm our commitment to the safety and security of Israel."

Congress will vote later this month on a resolution disapproving of the agreement. That bill is likely to pass, given the GOP majorities in Congress, but President Obama has vowed to veto it. Republicans would need to muster a two-thirds majority in both houses to override that veto, and Mikulski's declaration of support on Wednesday seems to close off that option to them.

The development marks a big foreign policy victory for President Obama and his administration, which has faced an avalanche GOP criticism on the negotiations with Iran. It also marks a stinging defeat for the opponents of the deal, who have spent months - and millions of dollars - trying to sink it.