If Congress fails to block the Iran deal, and it goes forward for the time being, one key player who will deserve credit for that is Senator Dick Durbin of Illinois. Durbin, the Minority Whip, came out for the accord early and has been working hard behind the scenes to round up support for it among Senate Democrats.

Sen. Dick Durbin (D-Ill.) speaks during a Senate Appropriations Committee markup in Washington last month. (Andrew Harrer/Bloomberg News)

Durbin tells me that after talking privately with most Senators in the Democratic caucus, there’s “no reason to panic” about the possibility that Congress might block the deal, adding that “only a few” have expressed serious resistance or opposition. “The response has been positive across the board,” Durbin says, adding that he doesn’t think the tens of millions of dollars opponents plan to spend on ads slamming the accord will ultimately have a real impact.

Due to the oversight framework Congress passed, if only one-third of one chamber of Congress sticks with President Obama’s veto of a GOP measure disapproving of the deal, it goes forward for now. If the White House loses more than a dozen Democratic Senators, the veto could get over-ridden, blocking it. A lightly edited and condensed version of my conversation with Durbin follows.

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THE PLUM LINE: You’re playing a major role in trying to round up support for the Iran deal inside the caucus.

SENATOR DURBIN: I’ve been approaching my colleagues on a one-on-one basis. They started coming back to me and telling me how they felt about it. I’ve gone through probably two thirds of the caucus.  This is all being done in the official whip staff fashion. This is not a high-pressure sale.

The response has been positive across the board, with only a few exceptions. By the end of next week I’ll have a good handle on where our caucus is.

PLUM LINE: You say the reception has been positive across the board. The media narrative seems to be, “there are 12, 13 Democrats who might vote against this thing. It’s not impossible that the veto gets over-ridden.” What’s the reality?

DURBIN: The reality is, it is positive. I’m not going to cite numbers to you. But I will tell you that there’s no arm-twisting. And the response has been positive so far. There are a few exceptions, and most of them have said so publicly. There are some who are going through a longer process. I’m not hurrying anybody along. This is an important decision.

Based on my conversations, there’s no reason to overreact or panic.

PLUM LINE: We’re hearing that opponents are going to spend $20-40 million on ads against the deal. Is it possible they could shift the dynamic in August?

DURBIN: I would be surprised at this point. I don’t believe television ads are going to have an impact on the final decision.

PLUM LINE: What about the substantive criticisms of the deal? There’s the lifting of the conventional arms embargo, the $150 billion that could find its way into terrorists’ hands, there’s the 24 day problem. Aren’t these concerns?

DURBIN: No. These have all come up in questioning with the administration, and they’ve been handled very well. As Secretary Ernest Moniz said about the 24 days, it is difficult to erase the presence of fissile material, whether it’s 24 hours or 24 days. The $150 billion — many people think that figure is exaggerated and overlooks the real deficiencies within Iran’s domestic agenda. They have gone through sanctions and come up with money to support terrorist activities. I don’t think this money is going to translate directly into terrorist support.

PLUM LINE: Senator Angus King was quoted saying there are both substantive and political risks for Democrats in supporting this thing, because if Iran cheats, then Democrats will look like they signed on to something ineffectual. Is that a legitimate concern?

DURBIN: I respect Angus, but I would see it the other way. If Iran cheats, and is caught, that is exactly what this whole agreement is about. If Iran were to cheat and not be caught, then our critics would be right. But with the verification and inspection on the ground, that is extremely unlikely.

PLUM LINE: I haven’t seen Republicans who oppose this deal getting pressed on the consequences of blocking it. The way Republicans have framed the discussion, it’s as if there’s only one set of consequences that flows from supporting the deal.

DURBIN: There’s no alternative to this agreement. If for some reason it does not go through, and Iran closes the doors on their development of a nuclear weapon, how could Israel or any nation feel any safer?

PLUM LINE: Some of the polling has been favorable to the deal, but the Pew poll actually found disapproval. Are Democrats doing a good enough job of making it clear that the choices are this deal or war? Or are Republicans going to be able to muddy the waters and create the impression that there’s a third way?

DURBIN: All the briefings have been very clear. Absent an agreement, we believe Iran will set out to develop a nuclear weapon. If we confirm that progress towards a weapon, our alternatives will be limited. They could involve a military response. We don’t know how long or costly it would be. The unthinkable is that they would develop a weapon without a response.

PLUM LINE: But in the public domain, isn’t it on Democrats to make this as clear as possible?

DURBIN: Yes, of course it is. We can’t just let Republicans just criticize the agreement without at least suggesting what the alternative would be.