THE CLOCK is ticking toward expiration of the last major nuclear arms control treaty, New Start, which will end a year from now if not extended by the United States and Russia. Should it lapse, the path will be open to another dangerous arms race, hardly what the world needs. Right now, all signs are pointing in the wrong direction.

The New Start treaty, which limits the United States and Russia each to 1,550 deployed strategic nuclear warheads and 700 delivery vehicles, is set to expire Feb. 5, 2021. A five-year extension procedure was included in the treaty, and President Vladimir Putin of Russia has urged the United States to begin talks to implement it. Unfortunately, the Trump administration seems to be in no hurry. An extension is in the interest of both sides: The treaty provides for intrusive verification and ensures stability in nuclear arsenals.

If New Start lapses, both countries will be free to deploy more nuclear warheads and build new generations of weapons and delivery systems. While both have been steadily modernizing nuclear forces in asynchronous cycles, they were adhering to New Start limits. All bets are off without it. Russia has lately boasted of new programs such as a hypersonic glide vehicle, and the United States has confirmed deployment of a new, low-yield nuclear warhead, the W76-2, on a submarine-based ballistic missile. These developments are but a hint of what will come with unrestrained nuclear competition.

The new U.S. warhead is based on an unconvincing read of a possible Russian strategy for use of tactical nuclear weapons in combat. It would have been far better to negotiate a new treaty addressing these weapons — tactical nuclear weapons have never been subject to treaty limits — than to build a new warhead. But treaties appear to be out of fashion. The United States withdrew from the 1987 Intermediate-range Nuclear Forces Treaty last year because of Russia’s alleged violations; the sides were unable to resolve the issues.

The administration’s desire to include China at the nuclear weapons negotiating table is a worthy goal in the long run. But China, with its estimated 290 nuclear warheads, has said it won’t join negotiations until both Washington and Moscow, each with a much larger arsenal, get serious about reductions. Right now, demanding China be included looks more like a poison pill for New Start than a genuine attempt to keep the treaty alive. If the administration really cares about bringing in China, then speedy work toward a New Start extension would be a better signal to China about a future negotiation than letting the treaty lapse.

Arms control takes political willpower. Binding and verifiable treaties are worth the effort. The weapons themselves are as cataclysmic in their power as ever. Have we lost the willpower to keep them in check?

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