President Obama's hopes for Senate passage of his Iran deal received a body blow as New York senator Chuck Schumer announced he would vote against the agreement.

Schumer has a lot of clout in the party and has indicated he will lobby other Democrats to get them to oppose the deal.

Reuters:

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 July 1 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. He was the first Senate Democrat to announce his opposition to the agreement.

Another influential Jewish lawmaker, U.S. Representative Eliot Engel, the top Democrat on the House of Representatives Foreign Affairs Committee, also said on Thursday he would oppose the nuclear pact in 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.

Obama has been engaged in his own lobbying effort, including a combative speech on Wednesday in which he said abandoning the agreement would open up the prospect of war.

Speaking at a news conference on a visit to the Vietnamese capital Hanoi, U.S. Secretary of State John Kerry, who negotiated the deal on the U.S. side, said he respected Schumer and Engel but added that "rejection is not a policy for the future."

"It does not offer any alterative and many people in arms control and others have actually pointed that out. While I completely respect everybody’s individual right to make a choice, I obviously disagree with the choice made," he said.

The U.S. Congress has until Sept. 17 to consider a resolution of disapproval of the Irandeal, which would eliminate Obama's ability to waive all sanctions on Iran imposed by the U.S. Congress, a key component of the agreement.

Lawmakers will begin debating whether to reject the deal when they return from their August recess on Sept. 8.

Schumer's opposition will give at least some Democrats political cover to oppose it as well.  The same goes for Rep. Engel, who is one of the most respected foreign policy heads on The Hill.  With so many Democratic fence-sitters in both chambers, Schumer's and Engel's opposition sets an example that at least some lawmakers will follow.

Schumer says he will work to get other Democratic members to oppose the deal, but a whip count at this point shows up to 22 undecided Democrats.  That means that treaty opponents will have to convince more than half the undecideds to defy the president and vote to override his veto.

Clearly, Schumer has some work to do.

Thomas Lifson adds:

I wish I could agree with Rick, but I see this as a sign that the White House gave permission to Schumer to protect himself with his constituents because they know that a presidential veto will not be overridden.  Rather than a sign of weakness, it is a sign of strength.  Alas!