The push for a new Iran sanctions bill may have stalled in the Senate, but it’s still alive and kicking in the House, where leaders are telling members such a measure could still be considered this year. Indeed, proponents of more sanctions appear to be clinging to the hope that if something passes the House with broad bipartisan support, it could pressure the Senate to act.

But here’s something that could help block that from happening — in the process delivering yet another big blow to the prospects of a new Iran sanctions measure.

I’m told more than 70 House Dems — from a diverse ideological background — have now signed a new letter coming out against any new sanctions measure and calling for diplomacy to be given a chance. This represents the first public statement from House Dems en masse against the measure and for diplomacy, matching what we’ve been seeing in the Senate. Here’s the text, which hasn’t yet been released but was sent over by a source:

Dear Mr. President:

As Members of Congress — and as Americans — we are united in our unequivocal commitment to prevent Iran from obtaining a nuclear weapon. The proliferation of nuclear weapons in the Middle East would threaten the security of the United States and our allies in the region, particularly Israel.

The ongoing implementation of the Joint Plan of Action agreed to by Iran and the “P5+1 nations last November increases the possibility of a comprehensive and verifiable international agreement. We understand that there is no assurance of success and that, if talks break down or Iran reneges on pledges it made in the interim agreement, Congress may be compelled to act as it has in the past by enacting additional sanctions legislation. At present, however, we believe that Congress must give diplomacy a chance. A bill or resolution that risks fracturing our international coalition or, worse yet, undermining our credibility in future negotiations and jeopardizing hard-won progress toward a verifiable final agreement, must be avoided.

We remain wary of the Iranian regime. But we believe that robust diplomacy remains our best possible strategic option, and we commend you and your designees for the developments in Geneva. Should negotiations fail or falter, nothing precludes a change in strategy. But we must not imperil the possibility of a diplomatic success before we even have a chance to pursue it.

Dem Rep. Lloyd Doggett — a senior member of the House Ways and Means Committee who spearheaded this letter along with Dem Rep. David Price – tells me in a statement:

“Iranian hard liners may ultimately obstruct a meaningful permanent agreement, but Congress should not give them a pretext for doing so. The support for this letter from a broad and growing coalition of more than 70 Members sends a strong signal that Democrats stand for peace and diplomacy.”

Aides who have seen the letter tell me it’s been signed by some prominent Jewish Democrats and at least one member of the Dem leadership (James Clyburn).

This comes after former Secretary of State Hillary Clinton (belatedly) weighed in against the sanctions bill, another blow to its prospects. While it does appear that the push for a sanctions vote has run aground, it’s worth reiterating that if something goes wrong in the talks, those who want a vote — including Republicans who appear to be using this as a way to divide Dems, and Democrats who refuse to be swayed by the administration’s insistence that a vote could derail diplomacy — could have a hook to revive their push.

Eric Cantor is still said to want to move an Iran sanctions bill, and Dems have been wary of the possibility that Steny Hoyer — the number two Dem in the House — could join Cantor’s effort, thus giving it bipartisan legitimacy and perhaps leading more Dems to support it. The new letter from around six dozen House Dems opposing such a move could make that outcome that much less likely — particularly if it continues to pick up more signatures.

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UPDATE: Dem Rep. Keith Ellison, who has also been organizing against the Iran sanctions vote, emails over a statement:

“A large number of House Democrats are unified against actions that could undermine diplomacy. Negotiations with Iran are complex and we may not reach a final agreement in exactly six months, but we’re the closest we’ve ever been to preventing Iran from acquiring a nuclear weapon.”

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.