Barack Obama securing enough support from Congress to support the Iran nuclear deal represents the final domestic hurdle for the US president, leaving the fate of the agreement in the hands of the United Nations.

Obama has faced strong opposition from Republican lawmakers who control both the House of Representatives and the Senate, but the public support of Democratic Senator Barbara Mikulski – the 34th senator to back the deal – has pushed the deal over the line.

Obama now has enough support to veto any motion to overturn the decision to lift US sanctions, with the Republicans requiring two thirds of the 100-member Senate to overcome a presidential veto.

The planned resolution of disapproval represented the last chance for domestic US opponents of the deal to stop it in its tracks.

The motion also represented Israel’s biggest hope to derail the agreement through the influential American Israel Public Affairs Committee (Aipac), a lobbying group that holds significant sway among sections of the US legislature.

Approval for the Joint Comprehensive Plan of Action (JCPOA) signed in Vienna on 14 July now largely hinges on assessment from UN nuclear watchdog the International Atomic Energy Agency’s (IAEA).

The IAEA’s assessment of the possible military dimensions of Iran’s nuclear programme is due to be submitted by 15 December. According to a source from the IAEA recently speaking to MEED, this could be approved quickly by the UN in a single board meeting.

With the issue of approval from Washington out of the way the deal now faces just one more hurdle over the next three months and could, if approved, pave way for the lifting of sanctions by the end of 2015.

The perceived success or failure of the nuclear deal years down the line will go some way to sealing Obama’s foreign policy legacy, which will also count rapprochement with Cuba among its potential success stories.

Obama will push for further support from the Senate to increase the legitimacy of his decision to push ahead with a deal that has split Congress and domestic public opinion. If supporters can rally 41 votes in favour of the deal then they will be able to block any disapproval resolution from the Republicans, leaving presidential veto unnecessary.

If Obama can push through the decision without the need to overrule congress, he can claim a stronger mandate when history judges the 44th president’s watershed decision on the country’s long-running Iran problem.