The White House fired a shot across the bows of New York senator Chuck Schumer on Friday for defying its position on Iran, warning that fellow Democrats on Capitol Hill may remember his voting record when deciding who to elect as their next leader.



Though Schumer’s announcement that he would vote in disapproval of the nuclear deal – which leaked mysteriously during the middle of the Republican debate on Thursday – is unlikely to derail the process, it represents an embarrassing rift with a senior Democrat who had once been one of Barack Obama’s staunchest allies.

Schumer is expected to take over as leader of the party’s caucus in the Senate when Harry Reid, currently the minority leader, steps down after the next presidential election.

But he has defied the president before on a critical issue, questioning last year whether it was right to expend so much political capital pushing through Obama’s signature healthcare reform, the Affordable Care Act aka Obamacare.

This time, Schumer’s opposition to the Iran nuclear deal also coincides with a number of other prominent defections by New York Democrats, including Bronx congressman Eliot Engel, who is also ranking minority member of the House foreign affairs committee.



The White House put a brave face on their defections during the last press briefing before Obama departs for a two-week vacation on Martha’s Vineyard, pointing out that more than 12 Democrats had come out in favour of the deal including junior New York senator Kirsten Gillibrand.



“[Schumer’s] announcement was not particularly surprising to anyone here at the White House, even if it was disappointing,” said press secretary Josh Earnest.



Earnest also distinguished Schumer’s opposition from that of Republicans, which it says is “ideologically driven” and “making common cause with hardliners in Iran”.

But the argument that Schumer’s opposition is more considered since he waited until reading the deal before announcing his opposition also raises the question of whether his criticisms should be taken more seriously by other Democrats.

In a calmly worded blogpost defending his decision, the New York senator – who is heavily backed by many Jewish American groups and historically close to Israel on many issues – rejected the notion that opposition to the nuclear deal was the same as favouring military strikes against Iran instead.

“I will vote to disapprove the agreement, not because I believe war is a viable or desirable option, nor to challenge the path of diplomacy,” wrote Schumer. “It is because I believe Iran will not change, and under this agreement it will be able to achieve its dual goals of eliminating sanctions while ultimately retaining its 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,” he added.

More than two-thirds of both the House and Senate are required to override a presidential veto of their vote of disapproval and so far few commentators expect enough Democrats to break ranks to make this possible.

Nonetheless, the White House and its allies appeared to be trying to drive a wedge between Schumer and the rest of the caucus on Friday in a none-too-subtle dig at his credentials to lead the party after Harry Reid’s retirement.

“I certainly wouldn’t be surprised if there were individual members of the Senate Democratic caucus who would consider the voting record of those who want to lead the Democratic caucus,” said Earnest when asked about Schumer’s leadership ambitions.

Former Obama advisers and allies on the left of the party were less guarded, calling the decision a betrayal.

“We’re going to get the Iran deal done with or without Senator Schumer or anyone else who insists on being trapped in the past when it comes to conflict resolution in the Middle East,” said Democracy for America executive director Charles Chamberlain.

“Senator Schumer was wrong when he voted to back the war with Iraq, and he’s wrong to work with Republicans to kill this nuclear deal with Iran, period.”

Earnest denied the White House had been involved in the leaking of the decision during the GOP debate, but sources close to Schumer told reporters that Obama was the only one who had been informed of the pending announcement at the time.