Barack Obama and Russian President Dmitry Medvedev sign the new Strategic Arms Reduction Treaty (START) in Prague on April 8, 2010. (Joe Klamar/AFP/Getty Images)

THE BIOLOGICAL and Toxin Weapons Convention, a treaty outlawing the development and production of germ weapons, lacked effective verification and compliance mechanisms from the moment it entered into force in 1975. A series of review conferences has tried to improve it, without much success. The eighth conference, just concluded in Geneva, fell flat.

Thanks largely to disruptive moves by Iran, participants said, the conference ended without agreement on a detailed work plan until the next conference in 2021, omitting the meetings of experts that could be so important in tackling recent advances in the life sciences, including genomics and synthetic biology. While the treaty remains in effect, the dismal outcome of the conference reflects a growing and worrisome trend in arms control. Treaties negotiated late in the Cold War and just after it are under stress. They were never an ironclad guarantee that nuclear, chemical and biological weapons would not be used, but they provided a certain stability and sense of confidence. These will be lost if the treaties are neglected.

In an article in Foreign Affairs, Michael Krepon, a co-founder of the Stimson Center, describes a period of “unparalleled achievement” from Ronald Reagan’s second term through the end of Bill Clinton’s. This included, among other things, the 1987 Intermediate-Range Nuclear Forces (INF) Treaty, two strategic arms limitations treaties, the Conventional Armed Forces in Europe (CFE) treaty, the Chemical Weapons Convention , the Comprehensive Test Ban Treaty and threat-reduction measures under the Nunn-Lugar legislation, as well as the 1991 initatives that unilaterally pulled back tactical nuclear weapons. Now, Mr. Krepon says, “all of this work is in peril” in a time of “great unraveling.”

The main reason is the tension in relations between the United States and Russia, a rift that deepened over Russia’s instigation of violence and coercion in Ukraine, over a rollback of democracy by President Vladimir Putin, and more than two rounds of NATO expansion and increased U.S. missile defenses in Europe. This friction is real and cannot be wished away. Arms control has always been based on a certain degree of trust — witness Mr. Reagan and Soviet leader Mikhail Gorbachev — and is eroded without it.

The INF Treaty is clouded by U.S. allegations that Russia has flight-tested a new ground-launched cruise missile in violation. The CFE treaty is largely dead after Russia pulled out, saying the map of Europe had changed. The test-ban treaty has led to the creation of a globe-spanning network of monitors, but it has not entered into force because eight nations, including the United States, have yet to ratify it. The chemical-weapons treaty is one of the most successful mutililateral arms-control efforts of the era, yet its prohibition on chemical weapons is being sorely tested by their use in the Syrian war.

Nuclear, chemical and biological threats are not going to vanish. The world is safer with these treaties than without them. Where possible, they ought to be strengthened, rather than allowed to fall into disrepair.