Washington: US President Barack Obama’s hopes of preserving the nuclear deal between Iran and world powers were set back on Thursday when Chuck Schumer, one of the top Democrats in the US Senate, said he would the oppose the agreement.

Schumer’s opposition, announced in a lengthy statement, could pave the way for more of Obama’s fellow Democrats to come out against the nuclear pact announced on 1 July between the United States, five other world powers and Iran.

The New York senator is among the most influential Jewish lawmakers in the United States.

Another influential Jewish lawmaker, US Representative Eliot Engel, the top Democrat on the House of Representatives Foreign Affairs Committee, also said on Thursday he would oppose the nuclear pact, according to a statement obtained by Reuters.

Israeli Prime Minister Benjamin Netanyahu has been pushing lawmakers to oppose the nuclear agreement, which he considers a threat to his country’s survival. Some pro-Israel groups have also been spending millions of dollars on an advertising campaign to push members of Congress to vote no.

The US Congress has until 17 September to vote on a resolution of disapproval of the Iran deal, which would eliminate Obama’s ability to waive all sanctions on Iran imposed by the US Congress, a key component of the agreement.

Obama has promised a veto if it is passed by the House and Senate. Republicans would need dozens of Democrats to vote against Obama to override a veto so, while Thursday’s announcements are a blow to the president, opponents of the deal still face an uphill battle to enact a resolution.

Several Democrats in both the House and Senate have already come out in favor of the nuclear deal. Schumer’s colleague from New York, US Senator Kirsten Gillibrand, announced her support on Thursday.

Schumer said lawmakers would come to their own conclusions but he would try to persuade other senators to vote against the Iran deal. Schumer is currently the number three Democrat in the Senate and is in line to succeed Harry Reid as the party’s leader in the chamber when Reid retires in early 2017.

‘There are some who believe that I can force my colleagues to vote my way,’ he said.

‘While I will certainly share my view and try to persuade them that the vote to disapprove is the right one, in my experience with matters of conscience and great consequence like this, each member ultimately comes to their own conclusion,’ Schumer said.

A congressional aide said Engel would vote for a resolution of disapproval and also vote to override an Obama veto if the resolution passed Congress. However, Engel did not say he would lobby against the deal among other lawmakers.

Schumer’s opposition was first reported by the Huffington Post. He said in his statement he opposed the nuclear deal because he believed Iran would not change and that the deal would let it eliminate sanctions while retaining ‘nuclear and non-nuclear power.’

‘Better to keep US sanctions in place, strengthen them, enforce secondary sanctions on other nations, and pursue the hard-trodden path of diplomacy once more, difficult as it may be,’ Schumer said.