The United States has about 180 B61 gravity nuclear bombs based in Europe. They are the detritus of the cold war, tactical weapons deployed in Belgium, Germany, Italy, the Netherlands and Turkey to protect NATO allies from the once-feared Soviet advantage in conventional arms. But the cold war is long over, and no American military commander can conceive of their ever being used. Even so, President Obama has put $537 million in his 2014 budget proposal to upgrade these bombs. When all is said and done, experts say, the cost of the rebuilding program is expected to total around $10 billion — $4 billion more than an earlier projection — and yield an estimated 400 weapons, fitted with new guided tail kits so that they are more reliable and accurate than the current ones.

This is a nonsensical decision, not least because it is at odds with Mr. Obama’s own vision. In a seminal speech in Prague in 2009 and a strategy review in 2010, Mr. Obama advocated the long-term goal of a world without nuclear arms and promised to reduce America’s reliance on them. He also promised not to field a new and improved warhead.

But the B61 upgrade would significantly increase America’s tactical nuclear capability and send the wrong signal while Mr. Obama is trying to draw Russia into a new round of nuclear reduction talks that are supposedly aimed at cutting tactical, as well as strategic, arsenals.

Even if there is a case to be made for keeping the bombs in Europe as a sign of America’s political commitment to NATO (allied opinion is divided on whether the weapons should stay), many experts doubt that the B61 warheads need to be rebuilt now, if at all. Government-financed nuclear labs have a rigorous program for testing them to make sure they still work.