The new Republican leadership in Congress has indicated that new, punitive measures against Iran might be among its first orders of business, even though diplomatic talks with our international alliance are entering a promising new stage. If my colleagues are serious about restraining Iran’s nuclear ambitions, they will resist the temptation to intervene and instead let our negotiators finish the job.

Altering the terms or objectives of the talks would amount to moving the goalposts when the end zone is in sight – with potentially devastating consequences.

November’s four-month extension of the “P5+1” negotiations (called so because of the participation of the five permanent members of the UN Security Council plus Germany) confirmed both the difficulty of the remaining issues and the importance of continuing to negotiate. We are still several steps short of a complete and lasting termination of Iran’s nuclear weapons program, but the current interim agreement between Iran and the international community – known as the Joint Plan of Action (JPOA) – is a vast improvement over 18 months ago, when Iran’s nuclear program was still expanding and shrouded in secrecy.

While the JPOA is only a temporary agreement, Iran has complied with it and verifiably frozen and rolled back its nuclear program, demonstrating that it is willing to take negotiations seriously.

Congress could play an important oversight role while negotiators work to build on this progress and secure a verifiable and lasting nuclear agreement with Iran. But acting peremptorily to demand specific concessions from Iran could destabilize the diplomatic balance needed for negotiations to both continue and ultimately succeed. It would be unwise, for example, to lay out unrealistic or overly-specific requirements for a final agreement to be acceptable to Congress.

Likewise, the nuclear negotiating table is not the place to compel Iran to clean up its act on issues unrelated to nonproliferation. Iran engages in an array of behaviors that the US and the international community find unacceptable, such as persecuting political opponents and religious minorities, and supporting terrorist organizations like Hezbollah. But we must not insist that everything be solved before anything is solved; a nuclear agreement is and should be our first priority, and such an agreement could facilitate progress on other fronts.

Imposing new or less flexible economic sanctions – which has been proposed by a number of my congressional colleagues, including Senators Kirk and Menendez – could do great damage to our prospects for a nuclear agreement with Iran. New punitive action could strengthen Iranian hard-liners and make their withdrawal from the negotiations more likely. Acting unilaterally could also undermine the stability of our international alliance, and thereby actually weaken the existing international sanctions regime.

The existing sanctions are, of course, a major reason that Iran is at the negotiating table, and Congress should stand ready to reimpose and strengthen them should Iran violate the terms of the JPOA or any future nuclear agreement. But taking punitive action now could send a message that Congress does not stand behind the negotiators.

We cannot lose sight of the fact that a verifiable nuclear agreement with Iran would make our country, Israel, the Middle East and the world much safer. The nuclear talks with Iran could still crumble under the pressure of opposition and distrust both inside and outside Iran. But the United States and the international community must press ahead – because of the security that the removal of the nuclear threat would bring and the dire alternatives we’ll face if negotiations fail.