If you want a sense of whether Congress will or won’t stop the Iran deal from going forward, a good place to start is with Dem Rep. Eliot Engel of New York. As one of the most pro-Israel members of Congress and a well-respected voice on foreign affairs, he is one of a small number of House Dems who will be lobbied hard by supporters and opponents of the accord — and will be closely watched for clues as to whether enough House Dems will stick with Obama to sustain his veto of the expected GOP measure.

In an interview today, Rep. Engel said he thinks it will be “difficult” to stop the deal from going forward, though he said he didn’t think it was impossible. Engel noted he has serious concerns about the accord — but also indicated he was giving serious consideration to the administration’s case for it, which suggests there may be more political space for more moderate Dems to support it than previously thought.

“I think it’s difficult,” Engel told me, in a reference to whether opponents of the deal would be able to muster two-thirds of both Congressional chambers to over-ride Obama’s expected veto of a GOP measure disapproving of it. “There will be pressure on Democrats to sustain the president’s veto.”

“By and large, if every Republican votes No, you need 42 or 43 Democrats,” continued Engel, the ranking Dem on the House Foreign Affairs Committee. “I think it’s difficult, but not impossible, to override a veto.”

Engel said he has concerns about the deal, but also said he remains undecided. “The thing that most disturbs me about the deal is that it doesn’t really prevent Iran from having a nuclear weapon — it postpones it 15 years,” Engel said. “Iran is essentially legitimized as a nuclear threshold state.”

“One of the things that gives me the greatest pause is the fact that with sanctions relief, Iran is going to be awash in cash,” Engel also said. “They’re going to be able to increase the financing of all these terrorist groups throughout the Middle East.”

But, interestingly, Engel allowed that a key administration argument for the deal — that without it, Iran could develop a nuclear weapon far sooner, making it a nuclear threshold state right now — had some legitimacy. “There’s credence in that as well,” he said.

“I don’t denigrate what was done,” Engel continued. “The president genuinely feels that this is the way to go, and they have a case to make, and we need to listen and weigh it.”

The fact that Engel is going even this far is itself significant. Engel’s insistence on a tough stand towards Iran is unquestioned: He has co-sponsored a billthat would have vastly expanded Iran sanctions, and he was a lead author of arecent letter from members of Congress that expressed “grave and urgent” concerns about the course of negotiations over Iran’s nuclear program.

In our chat, Engel also took issue with Mike Huckabee’s incendiary suggestion that the Iran deal will march Israelis “to the door of the oven.”

“Mike Huckabee has been a strong supporter of Israel, and I welcome his support,” Engel said. “I do think his choice of words was less than smart. I don’t think that we should trivialize the Holocaust or compare everything to the Holocaust. I think he meant to be helpful, but I was not comfortable with the wording.”