Therefore, it is imperative that U.S. President Donald Trump and Russian President Vladimir Putin make progress on stalled nuclear arms control matters that are on the agenda when they meet in Helsinki, Finland on Monday.

Since the 1968 nuclear Non-Proliferation Treaty was signed 50 years ago, every U.S. president has engaged in nuclear arms control negotiations with Moscow to reduce the nuclear danger to the United States. While the size of Russia’s stockpiles has been reduced sharply as a result of these agreements, the catastrophic dangers posed by the U.S. and Russian nuclear arsenals is still too high.

Today, each side can launch as many as 800 city-killing nuclear weapons in a first strike within about 20 minutes of the “go” order from either president. Each side would have hundreds more nuclear weapons available in reserve for further counterstrikes. The result would be a global catastrophe. As then-presidents Ronald Reagan and Mikhail Gorbachev noted in their 1985 summit statement: “A nuclear war cannot be won and must never be fought.”

Clearly, it is vital that the world’s two largest nuclear-armed states maintain a stable relationship and avoid direct military conflict.

Unfortunately, relations between Washington and Moscow are at their lowest point since the mid-1980s, and their dialogue on nuclear arms control has been stalled since Russia rejected a 2013 offer from President Obama to negotiate further nuclear cuts, and since tensions arose over Russia’s 2014 invasion of Crimea. As the relationship with Russia has eroded, Russia has engaged in more assertive military exercises and more frequent overflights in or near Western airspace. As a result, there has been an increasing number of encounters between the Russian military and the U.S. and NATO forces. The risk of accidents and miscalculations that could escalate to an armed conflict is significant. Unfortunately, the latest round of U.S.-Russian strategic stability talks was postponed this year.

To make matters worse, the existing nuclear arms agreements already in place—the 1987 Intermediate-Range Nuclear Forces (INF) Treaty and the 2010 New Strategic Arms Reduction Treaty (START)—are now at risk and, at the same time, both sides have begun replacing and upgrading their Cold War-era strategic nuclear arsenals.

The INF Treaty helped end the Cold War by eliminating all U.S. and Russian ground-launched ballistic and cruise missiles with ranges between 500 and 5,500 kilometers. The U.S. has accused Russia in 2014 of violating the INF Treaty by testing a prohibited ground-launched cruise missile. In response, the Trump administration has proposed new, “more usable” low-yield nuclear options, some of which would also violate the treaty.

Meanwhile, the START agreement, which caps each side’s strategic deployed arsenals to no more than 1,550 warheads and 700 strategic delivery systems, will expire in February 2021 unless extended or replaced.

Without a positive decision to extend New START, there would be no legally binding limits on the world’s two largest nuclear superpowers for the first time since 1972. The risk of unconstrained U.S.-Russian nuclear competition, and even more fraught relations, would grow.

In a March interview with NBC, Putin voiced interest in an extension of New START or even possibly further cuts in warhead numbers. In April, the Trump administration announced it is pursuing a “whole-of-government review” about whether to extend the New START.

New START clearly serves U.S. and Russian security interests. The treaty imposes important bounds on the strategic nuclear competition between the two nuclear superpowers.

Failure to extend New START, on the other hand, would compromise U.S. intelligence on Russian nuclear forces, open the door to unconstrained nuclear competition, and undermine U.S. and allied security.

Fortunately, the treaty can be extended by up to five years (to 2026) by a simple agreement by the two presidents—without complex negotiations and without further approval from the U.S. Senate or Russian Duma, and without making an unwise concession to Moscow.

A resolution of the INF compliance dispute is a more complex but resolvable problem—but only with higher-level leadership from both the White House and the Kremlin. Trump and Putin could direct their teams to pursue special inspections to answer questions about the Russian ground-launched cruise missile of concern to the United States and develop solutions that resolve each country’s compliance concerns.

Some Republican lawmakers believe New START should not be extended so long as the INF dispute is unresolved. Sacrificing New START, given the transparency it provides, would only compound the problem and scuttle the chances of bringing Russia back into compliance with INF.

New START extension would also provide additional time for Trump, or his successor, to pursue negotiations on more far-reaching nuclear cuts involving strategic and tactical nuclear systems, an understanding about the limits of U.S. strategic missile defenses, and limitations on non-nuclear strategic strike weapons that both sides are beginning to develop.

If they achieve nothing else in Helsinki, Trump and Putin should relaunch the dialogue on strategic stability and pledge to reach early agreement to extend the New START agreement. If not, we may see the emergence of an even more dangerous phase in U.S.-Russian relations.

Lawrence Weiler is one of the U.S. negotiators of the 1968 Treaty on the Nonproliferation of Nuclear Weapons and the 1963 U.S.-Soviet Hotline Agreement. Daryl G. Kimball is executive director of the independent, non-partisan Arms Control Association.