The Obama administration appears to be on the brink of signing a nuclear deal with Iran. If it pulls it off, it’ll be its biggest diplomatic accomplishment in years, one likely to render America safer and tame a key source of instability in an increasingly consequential U.S.-Iran dyad.

If it doesn’t get blown up by Congress, that is. And if it does, the administration will, contrary to its endless protestations, be greatly to blame.

How else are we to explain the administration’s impending confrontation with Senate Foreign Relations Committee chair Bob Corker? Corker’s proposal to give Congress a vote on the Iran deal—a far more palatable approach than what many of his colleagues have tried—is likely to advance out of his committee next week, and the administration is scrambling to keep Democrats from supporting it. Multiple cabinet-level officials have personally reached out to wobbly senators. The measure would need to get thirteen Dems behind it if it’s to override Obama’s promised veto. Recent partisan confrontations over Iran have made such large-scale defections less likely, but the Corker bill’s defeat is no sure thing.

That it has gotten to this point, and that it is a confrontation with Corker rather than more hawkish senators like Mark Kirk or Tom Cotton, reflects a failure in the administration’s outreach to Congress. The talks with Tehran are rooted in a bullet-biting pragmatism: we have tried for years to attain the ideal of an enrichment-free Iran, and have failed; the administration has accepted that painful reality and worked to get the least dangerous Iranian nuclear program we can. Yet the administration has failed to accept a domestic reality it finds just as painful: it will need the support of a skeptical Congress—a skeptical, now-Republican Congress—to lock in a deal. That failure of pragmatism now endangers the deal Team Obama has worked so hard to get.

Nonsense, reply the administration’s boosters: We’ve tried to work with Congress, they wouldn’t play ball, and so we’ll be rightly resisting this attempt to encroach on our constitutional authority. They’re correct that the president has the right to conclude nonbinding agreements with other states, yet one wonders how enthusiastic the Iranians (ever sticklers about the letter of the international laws they elect to follow) should be about a soft commitment from their greatest foe on an issue of central strategic importance. Wouldn’t a binding agreement be more attractive to them—indeed, wouldn’t making the deal binding be a low-cost concession for us that could get us concessions on bigger things? There’s a rub, though—the Senate wouldn’t be out of line in wanting a vote on such a deal, and the administration would need to be on the winning side of that vote. That requires working seriously with Congress. By dodging Congress instead, the administration may have put itself in a weaker position at the negotiating table with Iran while making the deal more vulnerable on Capitol Hill. Some tactics!

There is another way to get that binding agreement: to negotiate a nonbinding agreement with the Iranians and then vote for a binding resolution on the agreement’s terms in the United Nations Security Council. America would then be required to comply with the Security Council’s resolution. This legal laundering would have no purpose other than bypassing Congress, so Congress would be quite furious if it were used on such an important issue, and will want to ensure it isn’t; in parallel, an administration cultivating good relations with Congress would want to rule it out. Indeed, in a healthy relationship, Congress would not even need assurance—such chicanery would be unthinkable.

That didn’t happen. Corker sent a letter to the president on March 12 asking whether the administration might take the UN route. The phrasing of his letter is telling: “There are now reports,” he says, “that your administration is contemplating taking an agreement, or aspects of it, to the United Nations Security Council for a vote.” The chairman of the Foreign Relations Committee should not learn such things from the press—and if the press is writing them, he should be able to dismiss them as baseless rumors. The administration, meanwhile, should not publicly hem and haw about whether it might take the UN path before dismissing it, and it should take every opportunity to make crystal clear that this is not on the table; the official White House response to Corker’s letter didn’t do that, even though an administration official had already ruled the UN path out in comments to Buzzfeed reporter Hayes Brown.

What makes all this reflect so poorly on the Obama administration is that Corker is clearly someone they can deal with. Like most Republicans and many Democrats, he’s been wary of the administration’s Iran diplomacy. But when the survival of the negotiations has been threatened by actions in Congress, Corker has diverted energy toward pragmatic alternatives that protect Congressional prerogatives but allow the talks to continue. He and the administration have, in other words, been fighting the same battle under different banners.

Consider the campaign in early 2014 to pass the Kirk-Menendez sanctions bill. At the time, the bill linked sanctions to areas of U.S.-Iranian disagreement that are outside the framework of the ongoing negotiations with Iran. The introduction of these issues into the talks would have been all but certain to prevent an agreement, and the imposition of new sanctions would have risked the Iranians walking away from the table while the rest of the world blamed America. The bill was a bad idea—and it had bipartisan support. As the White House scrambled to turn its allies on Capitol Hill against Kirk-Menendez, Corker made two deft moves that helped it block the bill.

First, he proposed scheduling a vote on the bill six months later, for the day after the negotiations expired. Critics pooh-poohed his proposal, saying that the bill would have been just as bad an idea six months in the future as it was in the present. That missed the point: Corker’s proposal undermined the best argument for quickly passing the bill—that U.S. negotiators needed more leverage in the talks in the form of the threat of more sanctions. A vote scheduled for the day after the talks expired would have given that leverage, and it would have avoided the potentially destructive effects of passing Kirk-Menendez immediately; further, a breakdown in talks in six months would likely have made the international environment much more favorable to tough new American sanctions.

Second, Corker pushed his own Iran bill, a milder measure designed to give Congress an up-or-down vote on any final Iran deal. The bill’s immediate effect was to create fissures among Congressional Iran hawks, winning Lindsey Graham as a cosponsor and, as Bloomberg’s Josh Rogin reported at the time, earning the favor of John McCain, who thought the Corker bill should come first because it would be more difficult to oppose.

Facing wavering Democratic support, the Kirk-Menendez proposal flopped, and Corker’s bill stayed in reserve. What’s happened since has vindicated Corker’s approach. Many of the extraneous matters in Kirk-Menendez that Corker’s bill eschewed had to be stripped out to make the sanctions proposal more palatable to Democrats, and it still hasn’t passed. All the while, Corker has been promoting his own bill, maneuvering carefully to make it the respectable alternative. Corker was one of seven Republicans who didn’t sign Tom Cotton’s letter to Iran’s leaders—a telling gesture, since the letter purported to defend the same Congressional prerogatives as Corker’s bill. Corker’s official excuse was that he was focused on winning over Democrats, and he “just didn’t view the letter as constructive” for that end: “I knew it was going to be only Republicans on [the letter]. I just don’t view that as where I need to be today,” he told Politico’s Burgess Everett and Michael Crowley. “My goal is to get 67 or more people on something that will affect the outcome.” Corker’s instincts were right. The Democrats pounced on the letter, and the antiwar portion of their base was energized. It’ll now be harder for Democratic hawks to side with the GOP.

Now, patient tortoise to Kirk-Menendez’s and Tom Cotton’s hares, his bill has become the new frontrunner among those resisting the administration’s Iran negotiations. The White House is once again sending its best to the Hill to take down a Republican initiative. The prospect of a vote on a final deal wouldn’t be such a threat if they’d already won over Congress. And the man they’re fighting is the very one who could have won that battle for them.

John Allen Gay, an assistant managing editor at The National Interest, is coauthor of War with Iran: Political, Military, and Economic Consequences (Rowman and Littlefield, 2013). He tweets at @JohnAllenGay. ​