Thomas Countryman urges the president to extend New START:

And yet, Trump hesitates even to open discussions with Moscow on the modalities of an extension. As is his habit, he wants more—a bigger deal. Specifically, he wants to see a more expansive treaty, one that covers not only strategic nuclear weapons but also smaller, low-yield “tactical” nuclear weapons. More ambitiously, he wants to bring China into a new treaty and establish limits on its nuclear arsenal. These are praiseworthy long-term goals that should be pursued. But Trump’s belief that China is currently interested in negotiations on a three-way nuclear arms control pact with Russia is a fantasy, much like his assertions that China bears the cost of U.S. tariffs, or that Mexico will pay for the U.S. border wall.

Much like the president’s feigned interest in a “better deal” with Iran, his interest in a “bigger deal” on arms control is just an excuse for hostility to the existing agreements. When he wants to renege on an agreement, he claims he is doing it because the agreement was supposedly inadequate and needs to be expanded. The expansion that he describes is so unrealistic that he can’t be serious, but the pretense of seeking an expanded deal provides political cover for an agenda that is purely destructive.

The president clearly has no desire to negotiate real arms control or nonproliferation agreements. If he were interested in that, he wouldn’t insist on making so many non-starter demands of the other governments. His unwillingness to offer anything meaningful to North Korea after a year and a half is further proof that he won’t settle for anything less than the other side’s capitulation. He seizes on the first pretext he can find to dismantle existing agreements, and in some cases he just violates the agreements for no reason at all. Trump has been heeding the bad advice of anti-arms control ideologues for the last several years, and that has meant that he would much sooner burn down the entire architecture of arms control rather than add anything to it. He seems personally predisposed to expanding the U.S. arsenal rather than keeping it under current restrictions, and that has allowed hard-liners to prevail time after time in getting him to scrap agreements that were working very well.

If New START isn’t renewed, it not only opens the door to a new arms race, but it will also have destabilizing effects on relations between the U.S. and Russia even if there is no new buildup:

Even if the U.S. and Russia don’t immediately build up their forces, the treaty’s monitoring and verification regime will be impossible to replace. The U.S. intelligence community has concluded that even the most advanced national technical means cannot substitute for the transparency provided by New START. Without it, Russian and American military planners will gradually lose confidence in their understanding of each other’s nuclear forces and intentions, incentivizing them to assume the worst-case scenario about their adversary’s nuclear capabilities and rush to match them.

Letting New START die is senseless and indefensible, and Trump could prevent the treaty from expiring with a minimum of effort. His refusal to keep the treaty alive will be one of the more consequential, damaging decisions he has made as president. We will be dealing with the effects of his irresponsible rejection of arms control for a long time to come.