It isn’t getting the same attention as the high-profile brouhaha over Donald Trump’s disgusting comments about John McCain’s military service, but a quieter and potentially more significant dispute has emerged between two of the Republican frontrunners over the Iran deal.

Scott Walker said: “We need to terminate the bad deal with Iran on the very first day in office.” Jeb Bush replied that, while he too opposes the deal, it’s unrealistic to expect that it can be terminated on the first day of a new presidency: “At 12:01 on January, whatever it is, 19th [2017], I will not probably have a confirmed secretary of state; I will not have a confirmed national security team in place; I will not have consulted with our allies. I will not have had the intelligence briefings to have made a decision. If you’re running for president, I think it’s important to be mature and thoughtful about this.”

The subtext: Walker thinks Bush is a squish; Bush thinks Walker is simplistic.

Who’s right here? Should terminating the agreement be the objective on day one of the next presidency?

As it happens, I think both candidates have a decent point. (Full disclosure: I have advised both candidate but haven’t endorsed either one.) Walker made his pledge not only to establish his conservative credentials in foreign policy but also to send a signal to European and other companies that might be thinking of doing business with Iran by calling into question whether the agreement with Iran will survive. Symbolically Walker is sending the right message of resolute opposition to the deal, and Bush is (inadvertently, I hope) creating doubts about whether opposition to the deal will be a defining feature of his administration.

But Bush is right that unraveling the accord won’t be simple—and not only because it will take a while for the next administration to get its foreign policy team in place. That’s actually the least of the problems.

For a start, there is the fact that the most effective sanctions on Iran are those imposed by our European allies through the United Nations. The U.S. has not done much business with Iran for years. We can re-impose unilateral sanctions, probably with the stroke of a president’s pen, but we cannot do the same with the multilateral sanctions that have truly put pressure on Tehran. If the next president is to have any hope of putting Iran back into the sanctions box, he or she will have to do some heroic diplomatic work to convince our allies to go along or else risk open economic warfare with our closest allies.

Imposing unilateral American sanctions would be just a symbolic move that would not seriously hurt Iran and could very well help it. The deal that Obama has reached makes clear that Iran will exit the treaty if the U.S. even thinks about re-imposing sanctions, thus escaping any limitations on its nuclear program. It could then dash to a nuclear breakout. By that point, Iran would have pocketed well over $100 billion in benefits, so it could have its cake and eat it too: getting both a nuclear weapon and a financial windfall. And it would be able to do so with at least the tacit support of the international community, because absent pretty clear evidence of Iranian cheating, Tehran would be able to blame the new American administration for destroying the deal.

This is an indication of what makes the current deal so pernicious — it will be very hard to escape. And yet, the major elements of the deal are likely to be implemented as soon as this week when the U.N. Security Council is likely to ratify the accord, thus dropping multilateral sanctions on Iran within probably six months or so. Congress will be unable to stop this move even if it can somehow muster a veto-proof majority to vote down the deal (which is unlikely).

The best bet for the next president could well be to calculate that, with the treaty at least placing some limitations on the Iranian nuclear program and with Iran already have gotten its financial windfall, it might be better to keep the accord in place while taking other steps to counteract Iran’s growing power grab (for instance, doing more to support moderate Sunnis across the region), reversing the decline in American defense spending which is hollowing out our military, and building the case, both at home and abroad, for re-imposing sanctions and even using force if necessary to stop the Iranian nuclear program (a credible threat of military action will be a prerequisite if there is any hope for renegotiating a better deal.)  In other words, to reassert the deterrence and containment of Iran.

To succeed at this difficult undertaking, the next president will need to create a comprehensive campaign, in cooperation with allies, and that is simply not going to be possible on day one. But laying the foundation can begin now, and that requires expressing resolute opposition to this deeply flawed treaty.