WASHINGTON, United States (AFP) — US President Barack Obama on Wednesday earned sufficient congressional backing to ensure the Iran nuclear deal does not get blocked, when a 34th senator announced her support for the accord.

Most US lawmakers are opposed to the deal, which would ease punishing economic sanctions on Tehran while preventing it from advancing its nuclear program. Many Republicans warn that the Islamic republic will seek to cheat its way to an atomic bomb.

But with Senate Democrat Barbara Mikulski announcing her support Wednesday, the deal now has 34 backers in the Senate — the number needed to uphold a certain Obama veto should Congress pass a resolution that disapproves of the deal.

Overcoming the veto would require a two-thirds vote in the Senate and House of Representatives.

While the deal is not perfect, Mikulski said, “I have concluded that this is the best option available to block Iran from having a nuclear bomb.”

Some Republicans have urged walking away from the deal and renegotiating tougher terms with Tehran, but US negotiators have warned that such a move could see the fragile international coalition that secured the agreement fall apart.

“It’s unclear if the European Union, Russia, China, India and others would continue sanctions if Congress rejects this deal,” said Mikulski, the longest-serving female senator in history.

“At best, sanctions would be porous, or limited to unilateral sanctions by the US.”

Republicans are unified in their opposition, warning that easing sanctions will provide Iran with a windfall of up to $150 billion, which they say could be funnelled toward terrorist operations.

“Iran deal done. With Mikulski, Obama has all the votes he needs,” number two Senate Republican John Cornyn posted on Twitter.