The Obama administration is entering its final months, but it’s never too late to further diminish U.S. influence and discomfit our allies.

President Barack Obama is considering adopting a policy of “no first use,” i.e., declaring that the United States would never use nuclear weapons except after a nuclear attack on itself or its allies. From Obama’s perspective, this change would have the dual advantage of being something he can legitimately do on his own and representing a radical departure in the country’s nuclear doctrine.

For 70 years, presidents of both parties have maintained a posture of nuclear ambiguity. We wanted enemies to have to contemplate the possibility of a U.S. nuclear response to acts of aggression. This added an extra element of uncertainty and risk to potential attacks on us or our friends, in the hopes of deterring them in the first place.

For the advocates of no first use, the very fact that ambiguity has been our policy for so long is a reason to abandon it. They urge that we get beyond “Cold War thinking,” a favorite line of President Obama’s as well. The end of the Cold War indeed changed the strategic environment, but it didn’t make nuclear weapons obsolete, or render age-old concepts like deterrence inoperative, or eliminate international conflict.

The paradox of nukes is that they are weapons of cataclysmic destructive force at the same time that they have proven to be a guarantee of peace. As the strategist Bernard Brodie wrote at the dawn of the nuclear age: “Thus far the chief purpose of our military establishment has been to win wars. From now on its chief purpose must be to avert them.” It is thanks in part to the advent of nuclear weapons that we have averted the total wars between great powers that made the first half of the 20th century a vast killing field.

Declaring no first use would kick away an element of our nuclear deterrent. Yes, we no longer have to worry about deterring a massive Soviet army facing west. But Vladimir Putin has already changed the borders of Europe through force, and there’s no reason to think he’s necessarily done. A RAND Corporation study says that Russian forces could reach the capitals of the Baltic States in less than 60 hours.

Why would we make Putin’s calculation any easier in considering such a move, or ease the minds of other potential aggressors like China and North Korea? We might never use nuclear weapons in response to a conventional attack, no matter how brazen. Obviously the risks in resorting to nuclear weapons would be mind-boggling, but taking the possibility off the table serves no purpose. If we are going to have nuclear weapons, we should take advantage of their deterrent effect.

Relying entirely on conventional forces for deterrence would require more military spending and more forward-deployed assets by us and our allies. Of course, the analysts and activists who argue for no first use tend to be the same ones who think we spend too much on defense. One of these things does not go along with the other.

Our allies are freaked out about the prospect of no first use. They have long relied on our nuclear umbrella, and if it is being pulled back, countries like South Korea and Japan will need to reconsider their decisions to forswear nuclear weapons. This is why no first use would contradict President Obama’s opposition to nuclear proliferation, and make Global Zero — the disarmament movement’s goal of a world free of nuclear weapons — even more of a pipe dream.

In short, there is nothing to recommend no first use unless you are a lame-duck president heedless of strategic reality and looking to make a gesture of anti-nuclear righteousness. No first use would make the world, at the margins, a more dangerous place — and be a perfect parting shot for President Obama.

Rich Lowry can be reached via e-mail: comments.lowry@nationalreview.com.