There was a spirited debate this month in the House Armed Services Committee over the wisdom of arming America’s ballistic missile submarine force with a lower-yield version of the thermonuclear warhead that has been standard since the Cold War.

The last Congress approved the plan as a deterrent to Russia, which is developing its own low-yield weapons, but the Democrats who now control the House voted to block the deployment of the less powerful warheads, arguing they are unnecessary and destabilizing.