Critics of U.S. negotiations with Iran over its nuclear program were quick to jump on comments made by Secretary of State John Kerry that Washington and Tehran still need to bridge some gaps in order to reach a comprehensive nuclear agreement. But that is not the full story.

While differences on key issues remain, progress has been achieved and an agreement is within reach if both sides remain focused and engage in creative, smart diplomacy. It is important at this critical stage in the process for policymakers in Washington to support the administration’s ongoing efforts at reaching a diplomatic solution, even if more time is needed to reach a good agreement that guards against a nuclear-armed Iran.

As Kerry noted in his Tuesday Vienna press conference, progress has been achieved in several key areas, both sides remain committed to reaching a deal, and negotiators are working in good faith to resolve the remaining differences.

But bridging the remaining gaps will likely require more time beyond Sunday target date to conclude the negotiations.

While a deal is within reach, congressional letters to the president like the one written by Sens. Robert Menendez, D-N.J., and Lindsey Graham, R-S.C., that set unrealistic expectations for the deal are unhelpful and send the wrong message to Iran.

The Menendez-Graham letter says that only full dismantlement of Iran’s illicit nuclear activities, including shutting down the Fordow enrichment facility and the Arak heavy water reactor, will block Iran’s path to nuclear weapons. This is an expectation that would only drive Iran away from the negotiating table.

These conditions are also unnecessary to prevent Iran from pursing nuclear weapons. The Arak heavy water reactor, which is still under construction, can be modified to produce less plutonium suitable for weapons. Iran has already stated publicly that it is willing to make these modifications and pledged not to build a facility that would extract the weapons-grade plutonium from the reactor’s spent fuel.

Under a deal with intrusive monitoring and verification any moves to deviate from these conditions would be quickly detected.

Shutting Fordow is also condition that Iran will not accept and an unnecessary measure. The facility could be re-purposed to house Iran’s research and development of centrifuges. If Iran is not producing and stockpiling enriched uranium at this facility, its location, deep inside a mountain, poses far less of threat. And again, Iran has demonstrated that it is willing to consider this option.

Failure to reach a good agreement is not an option. Some on Capitol Hill argue that a “bad deal is better than no deal.” In reality, a good deal is better than no deal, and a good deal is, with more time, still within reach. So Congress needs to do its part to help bridge those gaps — namely by supporting negotiations and an extension, not jeopardizing the prospects for a good deal with unreasonable demands.

Without a good agreement, there would be no constraints on Iran’s nuclear program. There would be less monitoring and oversight by the international community. Tehran could move to nuclear weapons far more quickly and with less chance of detection.

A year ago Iran’s nuclear program was expanding, talks with the Ahmadinejad regime had collapsed, and newly-elected President Hassan Rouhani’s commitment to a nuclear deal remained untested.

Over the past 12 months, Iran, the United States, and five world powers reached an interim agreement that has rolled back aspects of Iran’s nuclear program and halted its expansion in return for modest sanctions relief. Iran is now much further from a nuclear weapon than it was a year ago. Iran also is working with the International Atomic Energy Agency to answer questions about its past work related to nuclear weapons development.

In short, Iran is following through on its interim commitments, negotiating a comprehensive deal in good faith, and being more transparent about its past activities. All of these actions support Kerry’s assertion that Iran wants a comprehensive deal.

Negotiators may not be able to close all of the gaps before July 20. But a good deal that limits Iran’s nuclear program and puts in place intrusive monitoring and verification measures in return for relief from nuclear related-sanctions is in everyone’s best interest.

President Barack Obama said on July 16 that there is a “credible way forward” in the negotiations. So policymakers in Washington should do their part to support a deal — and the ongoing negotiations — that protects the national security interests of the United States. In the long-term, that means preparing to support a good deal by lifting sanctions in accordance with Iran’s compliance. In the short term, that means refraining from imposing additional sanctions and constraints on the deal, like the Graham-Menendez letter, and allowing US diplomats to negotiate an agreement that protects US security.

Kelsey Davenport is the non-proliferation analyst for the Arms Control Association, where she focuses on the nuclear programs in Iran and North Korea and nuclear security issues.