Could a low-yield, sub-launch nuclear missile stop a Russian first strike?

Could a low-yield Submarine Launched Ballistic Missile help stop a Russian-launched first nuclear strike by ensuring a proportional response and holding enemy targets at risk of a precise, tailored nuclear attack? Conversely, could a newly emerging low-yield nuclear weapon lower the threshold to a dangerous limited or large scale nuclear war? Could potential adversaries mistake a conventional cruise missile for a nuclear weapon -- and therefore launch a nuclear weapon?

via FOX News https://fxn.ws/2F6Hy4l