The White House on Wednesday said it was “encouraged” by growing support in the Senate for the Iran nuclear agreement, while stressing it would keep working with lawmakers to secure as much backing as possible.

“We are encouraged by the latest tally,” White House spokesman Josh Earnest said, according to Reuters.

“When the stakes are this high, every vote is important,” he added.

Earnest was speaking hours after President Barack Obama secured the necessary number of votes in Congress to ensure the passage of the Iran nuclear deal.

Democratic Senator Barbara Mikulski of Maryland became the 34th senator to declare her support Wednesday, saying that in her view the deal was the best way to prevent Iran obtaining nuclear weapons.

Her announcement came just one day after Senators Chris Coons (D-DE) and Bob Casey (D-PA) similarly declared their support, providing the White House with 33 out of the 34 votes it would need to maintain a presidential veto.

Obama will be using that veto if – as appears likely – the Republican-dominated Congress rejects the Iran deal by a simple majority.

Republicans are unified in their opposition to the Iran accord.

Two top Democratic senators – Chuck Schumer and Robert Menendez – are also opposed, as are a handful of Democrats in the House, including Steve Israel, the chamber’s highest-ranking Jewish member.

But that will not be enough to grant victory to the nuclear deal’s opponents, who argue it gifts Iran with all its key demands without actually ensuring it will not obtain nuclear weapons at a later date.