If you were President and Putin let fly the nukes, would you retaliate in kind?
I wouldn't. Russia could not contend with the military might of NATO regardless of nuclear retaliation, and Putin would likely incur the wrath of the world beyond all hope.
And, I could not morally live with the weight of the destruction regardless of who started it.
The major military powers know where each other's ground based nuke launch sites are. As retaliation, I would take out as many sites as I could with a counter strike. Some of this could be done without nukes; high speed penetration devices.
This leaves mobile nukes on submarines, trains, trucks and aircraft. The country will now need to be on full guard for their heat and radiation signatures. These can be seen from satellites. Another response will follow, if they mobilize, hoping to escalate.
Civilian targets would be off limit, even if there is a push to get even with the other country. I would allow a limited target strike on the leadership, to end this.
One of the problems is, rules are such that we do not go after the leaders who start trouble. Rather the conventional game is to scapegoat subordinates and the masses, who did not do the bad deed or were ordered to act.
This convention was created by all the corrupt leaders at a corrupt leader union meeting. I would not follow this nonsense convention, but would be go after the sources of crime. The masses do not have launch codes. Leadership and political targets would be next; kill the head of the snake. This last action can be stopped short, if those who started this, put on the brakes.