The nuclear deal that the United States and its international partners reached with Iran achieved what it set out to do: prevent Iran from building a nuclear weapon. This is not solely a White House talking point. Seventy-five nuclear experts have now voiced their support for the deal in addition to top U.S. scientists, generals and admirals,ambassadors, national security experts, and the Israeli security establishment — all of whom agree that the bargain will block all pathways for Iran to build a nuclear weapon.

The agreement is rock solid. As a joint bipartisan statement from a group of national security leaders says, “We . . . conclude that the JCPOA represents the achievement of greater security for us and our partners in the region.” Further, it states, the agreement “meet[s] all of the key objectives.” For instance, it disables Iran’s nuclear infrastructure, reduces Iran’s holdings of nuclear material by 98 percent, and places Iran’s facilities under the most stringent inspections regime ever negotiated. One nonproliferation expert said of this agreement that if Iran ever makes a move toward building a bomb, “the likelihood of getting caught is near 100 percent.”

Yet, critics of the Iran deal rarely, if ever, argue about the technical aspects of this accord. Instead, detractors — many of whom vigorously helped push America into war with Iraq — say that there is a better deal out there, if we just play hardball. Never mind that the agreement has been broadly endorsed by the international community or that it took nearly two years of painstaking negotiations to complete.

Indeed, one could dismiss these charges outright if Congress had not already provided itself with the opportunity to kill the deal. Rather, we must seriously examine the claim that a better deal exists, because if Congress were to prevent the president from implementing the current one, the United States will look weak and untrustworthy, the agreement will fall apart, and the chances for still more war in the Middle East may increase.

The notion that we can negotiate a “better deal” in the event that Congress kills the one agreed to in Vienna is pure fantasy for several reasons.

First, getting a “better” package would not only require the current international sanctions regime to remain firmly in place, but it would also need additional pressure from the international powers that got Iran to the negotiating table in the first place. Indeed, the unity of United States, Britain, France, China, Russia and Germany — a group that doesn’t agree on many things — made possible a final arrangement with Iran. If it is undermined by Congress, the entire sanctions regime will collapse, and with it, the pressure on Iran to comply with any restrictions on its nuclear program.

Second, if Congress trashes the deal, the United States would lose the credibility to negotiate a better one. Our partners will rightly conclude that if the United States can’t follow through on the transaction so laboriously built they would be unlikely to cement another one.

Third, even if by some miracle the sanctions regime and international unity did not collapse, the politics of this issue don’t appear to be changing any time soon. The Republican candidates for president seem opposed to diplomacy with Iran in any shape. On the Democratic side, a President Clinton, Sanders, or O’Malley would confront the same problem faced by President Obama now: a Republican majority in both Houses poised to stop at nothing to kill a deal.

The reality is that any notion of voting down this accord with the goal of negotiating a better one will put the future of resolving this critical matter diplomatically in jeopardy and increase the likelihood of military action. Sen. Mark Warner should support this agreement — as former Sen. John Warner does — because it represents the best chance without going to war that the United States has had, or will have, to prevent Iran from developing nuclear weapons.

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This column originally appeared in The Roanoke Times and is reprinted by permission of the author.

How to Defend the Iran Nuclear Deal

OurFuture.org editor Isalah J. Poole talks to Ploughshares Fund president and arms control expert Joe Cirincione.