One of the biggest international security challenges the White House and Congress must tackle in the coming year is how to prevent the possibility that Iran could build nuclear weapons.

The key is to verifiably limit Tehran’s capacity to enrich uranium to weapons-grade, produce plutonium, and put in place more extensive international monitoring to ensure compliance.

Under the 2013 interim agreement negotiated by the P5+1 (the United States, China, France, Germany, Russia, the United Kingdom, and the European Union) and Iran, key areas of its program have been halted, providing time for talks on a comprehensive solution. Meanwhile, tough international sanctions remain in place, but the United States and its allies agreed not to initiate new sanctions on Iran while the talks continue.

Last week, U.S. and allied negotiators resumed negotiations with their Iranian counterparts, reporting “limited progress” and another round of talks in early February.

There are still gaps that must be bridged, but the two sides are closer than ever before to a verifiable, long-term deal that would block Iran’s major potential pathways to nuclear weapons and guard against a clandestine nuclear weapons effort.

Unfortunately, the Republican-led Senate, with the support of some Democrats, is moving fast to approve additional sanctions against Iran that would likely blow up the negotiations and the opportunity to secure a deal that would stop Iran short of a dangerous nuclear weapons capability.

President Barack Obama, backed by British Prime Minister David Cameron, came out strongly against new Iran sanctions last week and has threatened to veto the bill.

There are a number of key Democrats and a few Republicans who would be needed to approve the bill – or overcome a veto – who remain undecided about the new Iran sanctions legislation. The decision should not be so hard: new sanctions are unnecessary and would be counterproductive.

The new legislation, the “Nuclear Weapon Free Iran Act of 2015,” is scheduled for consideration by Senate Banking Committee next week. It is generally similar to a failed bill – S. 1881 – introduced in late-2013 that would also have derailed diplomacy and undermined implementation of the successful interim deal.

Advocates of new sanctions, including Sen. Bob Menendez (D-NJ) and Mark Kirk (R-Ill.), say they just want to put more pressure on Iran and claim that additional sanctions will only go into effect if the P5+1 and Iran fail to conclude a comprehensive nuclear deal by their July 1 target date.

This ignores the fact that even if new Iran sanctions do not go into effect immediately, Congressional action to initiate new sanctions while the interim deal is still in force and while the talks on a comprehensive agreement are ongoing would directly contradict the terms of the 2013 interim agreement.

If the United States violates the interim agreement and talks fail, Iranian hardliners will demand that Tehran walk away from the negotiating table and, once again, ramp up its nuclear program and capability to produce nuclear weapons.

To make matters worse, if Washington is blamed for any breakdown of the talks, other countries may resume trade with Iran. That would dramatically reduce U.S. leverage and the prospects for a diplomatic solution, while increasing the risk of a military conflict with Iran.

As U.S. Ambassador to the United Nations Samantha Power said on Jan. 12, the administration opposes new sanctions at this time because "if we pull the trigger on new nuclear-related sanctions now, we will go from isolating Iran to potentially isolating ourselves."

Furthermore, contrary to the claims of its authors, the new sanctions approach would undermine diplomacy even if there is an agreement on an effective, long-term diplomatic solution by July 1. Among other problematic provisions, the new legislation would:

·         Re-impose any sanctions waived under the interim agreement if the president does not transmit the agreement and a “verification assessment” report, conducted in consultation with the Director of National Intelligence, within 5 days of “entering into” any comprehensive nuclear agreement or extension of the interim agreement with Iran. Completing such an assessment within five days would be extremely difficult and would likely lead to the automatic imposition of sanctions. This provision clearly is not a serious effort to consider the matter of verifiability but is instead just another device for trying to trip up the process and undermine the whole agreement.    

·         Bar the president from exercising his waiver authority on some existing sanctions, a step that may be called for under a comprehensive nuclear deal, because the bill requires a “30 day continuous session of Congress” review period. Because Congress does not meet continuously, this could effectively delay implementation of the comprehensive deal by at least two to three months.

Some proponents of the new sanctions, like Arkansas Republican Tom Cotton, admit that the real goal is to end the negotiations. In remarks to the Heritage Foundation on Jan. 13 he said: “…[T]he end of these negotiations isn't an unintended consequence of congressional action. It is very much an intended consequence, a feature, not a bug, so to speak.”

Members of Congress should understand that moving forward with additional sanctions at this time is not the smart way to “get tough” on Iran. In fact, it would make it far tougher to curb Iran’s nuclear capabilities.

Iran’s moderate leaders and its population are more eager than ever to dismantle the ongoing, punishing sanctions regime, which continues to hurt their economy. New U.S. sanctions at this time would only tip the political balance inside Iran to the hardliners who flourish in a “resistance economy” and who support an unconstrained Iranian nuclear program.

If the International Atomic Energy Agency determines in the future that Iran is not fulfilling its commitments under the interim agreement or if it rejects a reasonable, final P5+1 proposal for a comprehensive deal, Congress would still have the option to act quickly, and, if necessary, enact new and tougher sanctions.

But as long as Iran and the P5+1 are holding up their ends of the interim agreement and are within sight of an effective comprehensive agreement, Congress should support, not sabotage, the diplomatic opportunity to prevent a nuclear-armed Iran.

Daryl G. Kimball is the executive director of the independent, nonpartisan Arms Control Association in Washington, D.C.

Image: Official White House Photo by Pete Souza