Sanders’ expression of support for the deal brings the Democrats one step closer to securing the 34 votes necessary to prevent a vote to override Mr. Obama’s veto.

But Democrats in the House and Senate said they remained confident that a sufficient number would ensure Obama’s deal survives.

“I appreciate the incredible efforts President Obama and his administration have made to address the threat of Iran’s nuclear weapons program”, he said.

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.

That suggests Schumer isn’t trying to campaign against the bill, which would infuriate the White House even more, but is merely announcing personal opposition.

However, with Schumer and several leading Jewish House Democrats – including Rep. Eliot Engel, D-N.Y., ranking member of the House Foreign Affairs Committee – opposing the plan, the president could have a tougher road getting it approved in Congress.

Obama is struggling to gain congressional backing for the deal, which lawmakers must vote on by September 17. Other Republicans, like Pennsylvania Sen.

“In future years, many would argue as long as Iran appears to be complying with the agreement, America can not insist on modifications or extensions of nuclear restrictions”, he said.

Meanwhile, Israeli President Reuven Rivlin warned on Friday that Prime Minister Benjamin Netanyahu’s fight with Washington over the Iran nuclear deal threatens to leave the Jewish state isolated. “If this prominent Democrat comes out and declares the deal bad for Israel, other Democrats are going to feel pressure not to contradict him”, Max Fisher wrote. A source told Politico Schumer had informed the White House of his decision but planned to announce it publicly on Friday.

Schumer’s split with Obama is remarkable for a senior leader in line to replace Senate Minority Leader Harry Reid of Nevada after Reid retires at the end of next year.

“Senator Schumer at least read the agreement, talked to the experts who were involved in negotiating, spent time talking to experts who understand the nuclear basis for some of the strategic conclusions that were reached by our negotiators”, Earnest said.

“The momentum is behind this deal, as you’ve seen from Democrats coming out this week”, spokesman Ben Marter said. Schumer and New Jersey Democratic Senator Bob Menendez, who has been critical, are expected to vote with the 54 Senate Republicans likely to stand united against the deal, but that is still leaves the GOP four votes short of overcoming a Democratic filibuster. Schumer’s decision outraged some liberal groups, who called him a “warmonger”, dismissed the notion of Schumer as the next Senate Democratic leader and vowed to withhold contributions from Democrats opposed to the deal.