Sanctions on Russia have progressed along the lines of the economic pressure campaign against Iran: the heavy measures, the transatlantic coordination, the questions about energy security, all happening again—but at record speed. Now, in another echo of the Iran experience, Congress wants to get involved in Russia sanctions. But Congress should refrain from passing its own sanctions: they will have limited effect and harm diplomacy.

The pace of U.S. sanctions on Russia has been unprecedented. For the past three weeks, Washington has imposed heavy measures on Moscow, targeting ever greater segments of its economy. Last week, the Biden administration banned imports of Russian oil into the United States, following similar moves by Canada, Australia, and the United Kingdom.

Against this backdrop, Congress has also tried to impose statutory measures. Last week, the House of Representatives passed its own oil import ban. Individual members have proposed additional sanctions. Sen. Ron Wyden, for example, has floated stripping tax credits for companies doing business with Russia. Sen. John Cornyn introduced a bill that would impose secondary sanctions on foreigners who purchase or transport the Russian central bank’s gold.

Congress should refrain from these steps. Their benefits would be paltry. Russian oil imports are already banned under Biden’s Executive Order 14066, so Congress would hardly be turning the screws. And while the other proposed measures might have incremental effects, they are unlikely to significantly change Russia’s calculus. None of them, for example, were included in a recent survey by two former State and Treasury Department officials listing outstanding pressure points. Indeed, the most significant economic damage to Russia would come from foreign jurisdictions cutting off their economic exchange with Moscow, something mostly outside of Congress’s power.

But while the benefits of congressional sanctions would be limited, the downsides could be great. In short, these measures could interfere with the basic functioning of U.S. economic pressure on Russia.

At their core, sanctions are bargaining measures. As Under Secretary of State Victoria Nuland has stated, if Russia complies with U.S. demands for a peaceful resolution, the United States will offer Moscow sanctions relief in exchange.

Washington cannot control whether Russia will accede to its demands, but it can ensure that any sanctions relief it does offer during future negotiations is credible. If Russia thinks that U.S. promises are empty and that it will not reap any economic benefit from acceding to western demands, it will be less likely to change its behavior. With sanctions relief uncertain, for example, Moscow might be unlikely to commit to an “irreversible” withdrawal from Ukraine, a condition recently articulated by Sec. of State Antony Blinken.

The president is well-positioned to ensure U.S. credibility. Through the International Emergency Economic Powers Act, Congress has given the executive branch the authority to impose and lift sanctions with few procedural hurdles. This power has not been without controversy. In these pages, former Treasury official Adam Smith, for example, has highlighted these measures’ “unfettered” nature and called for reform.

This very “unfettered” nature, however, is what makes sanctions so useful. The executive branch is responsible for the conduct of diplomacy – it makes sense for the same branch of government to make the promises necessary to achieve diplomatic breakthroughs, and then have the full capacity to fulfill them. This is why being able to quickly lift the sanctions imposed as part of a diplomatic strategy is essential to U.S. credibility.

Statutory sanctions put in place by Congress complicate this process. When sanctions are imposed by statute rather than executive order, the promise to lift them if the behavior of the sanctioned state changes is much less credible. For example, the president may need to make a provisional diplomatic agreement, and then ask Congress to actually deliver the U.S. end of the bargain, before being able to implement it in practice. That could be disastrous in the case of negotiating a cessation of hostilities. During the Obama administration, for example, Congress gave itself the power to stop the lifting of sanctions on Iran, complicating the negotiation and implementation of the nuclear deal with the world’s major powers and Tehran. In 2019, Congress tried to thwart an agreement to lift some Russia sanctions (thereby softening tensions with allies and restoring stability to global aluminum markets) after the Trump administration had already finalized it.

To be sure, congressional sanctions usually do give the executive branch some flexibility. The House oil import ban, for example, allows the president to waive the sanctions for “national security” reasons. Even with a waiver available, though, U.S. credibility is in jeopardy. Congress can override the presidential waiver, sending the message to Moscow that administration’s word is not the final one.

Moreover, even when waived, congressionally-imposed sanctions measures remain on the books. The oil import ban would stay in place—albeit suspended—potentially dissuading companies from rekindling business with Russia, the very carrot that Washington would seek to provide in exchange for Moscow’s cooperation. Another bill would require Biden to renew every 90 days a sanctions exemption that makes possible European energy purchases from Russia, creating uncertainty not just for businesses but for allies as well. There is precedent for similar waivers harming U.S. diplomacy. Following the 2015 nuclear agreement, the constant concern that the United States might suspend the sanctions waivers chilled Iran’s re-entry into the global economy, leading to complaints from Tehran that it was not enjoying the full fruits of its cooperation.

Indeed, the provisional nature of waivers can create pressure to reimpose sanctions. Were U.S.-Russia tensions to flare up again, the push to revoke the waiver and let the oil embargo come back into effect might be irresistible—essentially locking in a highly escalatory measure when a different response might be more appropriate. The very calendar of these renewals creates its own momentum. The Trump administration, for example, took its major steps to exit the Iran nuclear deal around deadlines imposed by the Iran congressional sanctions waiver schedule.

Congressional sanctions thus go beyond questions of symbolism or increasing economic pressure. As Elizabeth Rosenberg, now a top Treasury Department sanctions official, put it at a time when Congress was limiting President Trump’s ability to lift Russia sanctions, the fight over congressional sanctions is a “war over who controls U.S. foreign policy.”

However, the relationship between branches need not be so competitive. Congress alone has the power of the purse and ability to pass the spending bills that enable the United States to provide Ukraine desperately needed support for its military and to avoid a humanitarian crisis. In his State of the Union, Biden promised that the United States would offer this support to Kyiv—and last week Congress delivered by passing $13.6 billion in aid. Similarly, Congress alone has the spending power necessary to bolster sanctions resilience, a power it could use to cushion the U.S. economy from the supply chain disruptions caused by the economic campaign against Russia.

Congress should let Biden direct U.S. sanctions policy and focus on its most important and indispensable role—providing the money that both the Ukrainian people and the U.S. economy need to weather the storm.

Image: U.S. Capitol on February 28, 2022 in Washington, D.C. (Photo by Justin Sullivan/Getty Images).