COLLEGE PARK – Sen. Barbara Mikulski became the 34th senator to back President Barack Obama’s nuclear agreement with Iran on Wednesday, essentially ensuring that the controversial deal will not be stopped by the Senate.

In this March 2, 2015 file photo, Sen. Barbara Mikulski, D-Md., the longest-serving woman in the history of Congress, speaks during a news conference in Baltimore. Senate Democrats have rallied the 34 votes they need to keep the Iran nuclear deal alive in Congress, handing President Barack Obama a major foreign policy victory. Mikulski became the crucial 34th vote Wednesday morning, declaring the agreement is the best way to curb Iran’s nuclear ambitions. (AP Photo/Steve Ruark)

The Maryland Democrat’s backing means Congress will not have the two-thirds majority required to override a presidential veto of legislation opposing the Iran deal.

Until today, it was not guaranteed that the oft-debated deal would make it through the Senate. As of Wednesday afternoon, 56 senators — 53 Republicans and three Democrats — were against the deal, while 34 senators — Mikulski, 31 other Democrats and two independents — were in favor of the deal, with 10 senators — including Maryland Democrat Ben Cardin — still undecided.

“No deal is perfect, especially one negotiated with the Iranian regime,” Mikulski said in a statement Wednesday morning.  “I have concluded that this Joint Comprehensive Plan of Action is the best option available to block Iran from having a nuclear bomb.”

Mikulski announced her decision while Cardin was discussing the Iran nuclear agreement at a University of Maryland School of Public Policy roundtable with faculty and students.

Cardin has not yet indicated how he will vote. On Wednesday, the senator lauded Mikulski for taking the time to make an informed choice. “This is not an easy decision,” he said.

“I will make a decision shortly, Congress returns on Tuesday,” Cardin added. “It is unclear what’s going to happen if we go forward and unclear what’s going to happen if we don’t go forward. It’s important to acknowledge that.”

Cardin is the ranking member on the Foreign Relations Committee and also has strong ties to both the Jewish community and Israel, one of the countries strongly opposing the Iran deal.

Although Obama now has enough votes to sustain a potential veto, each of the 10 undecided senators has the ability to influence the deal. If seven of the remaining 10 senators back the deal, senate rules would likely prevent legislation opposing the deal from passing, meaning Obama would not have to veto it.