Foreign ministers from Iran and six world powers met Monday in a final push for a preliminary agreement, less than two days before the deadline to reach a deal limiting the scope of Iran's nuclear program. (Reuters)

The negotiations over the future of Iran’s nuclear program are coming down to the wire, with last-minute snags developing around the question of whether Iran will agree to allow its atomic fuel to be shipped out of the country. Other unresolved issues include the pace at which sanctions would be lifted, how many centrifuges Iran could continue operating, what research and development would be allowed on more advanced centrifuges, and what monitoring would look like.

But even if the framework of a deal is reached in the short term — the immediate goal of the talks — there is a real possibility, the White House believes, that Congress could kill a final deal even before it is agreed upon, with the willing participation of Senate Democrats. Republicans are widely expected to oppose the deal, whatever is in it. But even some Democrats who may support the deal could end up helping to scuttle it.

Here’s how. In mid-April, the Senate may vote on the Bipartisan Iran Nuclear Agreement Review Act of 2015 — a bill that is co-sponsored by Republican Bob Corker and at least eight Senate Dems, which puts it in striking distance of a veto-proof majority. The measure would require the president to submit any final deal with Iran to Congress within five days, and prohibit the suspension of sanctions on Iran for another 60 days, during which Congress could vote to approve or disapprove the deal.  A vote of disapproval would prevent the lifting of sanctions and thus cut off the ability of the U.S. to meet its end of the bargain. Even if Congress ultimately approved it, the 60-day wait would delay implementation of the deal.

The idea behind the Corker measure is to give Congress more oversight over the process — a laudable goal. But it’s unclear whether this bill is even needed to accomplish that: After a final deal is reached, Congress could theoretically vote to block it at any point it wished, even without passing the Corker measure first. The only practical impact of voting for this bill in mid-April might be to kill the deal before it’s even signed, by signaling possible Congressional opposition before it is finalized in a few months. Indeed, voting for this now might allow members of Congress to kill a compromise — without actually voting against any specific deal — under the guise of voting for more Congressional oversight.

To understand why, I spoke to Edward Levine, a legislative analyst on the Intelligence and Foreign Relations committees for over 30 years who has done some of the most in-depth analysis of the proposal out there. A lightly edited and condensed version of our conversation follows.

THE PLUM LINE: What would the Corker bill actually do?

EDWARD LEVINE: The Corker bill sets up a situation in which any final agreement with Iran has to be reported to Congress very quickly, which would deny Congress the benefits it usually has when considering something like a treaty, including a legal analysis and a verification assessment that often take several weeks to do. This would encourage Congress to take action before it really knew the details.

And Congress is encouraged to have a vote on the agreement within 60 days, during which the administration wold not be allowed to lift sanctions. That would push Congress to act quickly, before it really knew the details.

PLUM LINE: Why does that 60-day period pose a danger to a final deal? Would the passage of this in mid-April itself undermine the prospects for the final deal?

LEVINE: From the standpoint of U.S. negotiators, anything that suggests that Congress will not allow the U.S. to live up to its obligations makes it more difficult to get Iran to agree to anything in the first place. The primary danger is that hard-line decision-makers in Tehran will say, “to heck with this, we can’t trust the Americans to keep to their deal, so at a minimum we should demand more concessions in the talks, or we should just walk away.” If they are convinced the U.S. will never lift its sanctions, then what’s it in for them?

The Supreme Leader has the final say on whether there will be an agreement. The hard-liners are telling him, “we don’t like this deal. We don’t trust the other side to make good on sanctions relief. Unless you get all the sanctions lifted right up front, they are going to double-cross you.”

PLUM LINE: Supporters of the bill argue that all it does is give Congress more oversight over this process. But whether or not it passes this bill, couldn’t Congress at any point, or at any moment, vote down any final deal?

LEVINE: If they have the votes, yes. If Congress has the votes to override a veto, it could pass whatever it wants to pass.

PLUM LINE: I would like to see more Congressional involvement in foreign policy. But it’s unclear to me whether this bill is necessary to accomplish that in this case.

LEVINE: It is not necessary. Congress doesn’t need this bill to stop the deal. If an agreement is reached with Iran, anyone in Congress can introduce a bill saying the president is hereby barred from implementing it.

PLUM LINE: Isn’t it actually politically easier for a Democrat to support the Corker bill, in the name of enhancing Congressional oversight, than it would be to vote against an actual final agreement?

LEVINE: Assuming that the agreement is a good one, you’re correct.

PLUM LINE: Is there a more constructive way that Congress could vote to enhance its own oversight without voting for these provisions, which appear likely to scuttle an agreement even before Congress votes on the agreement itself?

LEVINE: Yes. There are several versions of that floating around. You could set up a process that does not have an initial timeline that forces Congress to consider the agreement before they had full information on it. If you are willing to accept the possibility that the administration could lift some sanctions now, and then a few months down the road, Congress, having gotten fuller information, could decide to reimpose some sanctions, then you avoid the need to act precipitously.

PLUM LINE: Are there any other ways this bill could kill a final deal?

LEVINE: One big way is by raising the possibility that Congress would reimpose nuclear sanctions even if Iran obeyed a nuclear deal completely. The Corker bill would also require the president to certify every 90 days that Iran has not directly supported a terrorist act that caused harm to an American or an American business. There would then be the option to introduce a bill reimposing all the lifted sanctions, and that bill would proceed with expedited procedures. For Iranian hard-liners, this means that even if the deal is a good one, and even Iran obeys it completely, Congress reserves the right to not let the U.S. implement sanctions relief.

Now, Iran’s support of terrorism is an important issue; we sanction Iran for that, too. But these negotiations have never had anything to do with terrorism. They have to do with a nuclear agreement, to forestall Iran from developing nuclear weapons.

PLUM LINE: Putting aside the Corker bill, Congress would have to vote at some point on lifting the sanctions, right? How does that all work?

LEVINE: We have a wide range of sanctions laws against Iran. As a rule those laws allow the president to suspend or waive sanctions for some period of time, but not permanently. If the U.S. wants to permanently end sanctions against Iran on nuclear grounds, then this has to come back to Congress.

PLUM LINE: If Senate Democrats support the Corker bill, is there a real danger that it could kill the possibility of any final deal with Iran?

LEVINE: Yes. Absolutely. Not intentionally, perhaps, but the danger is there.