The solution is to overwhelm the system of the one you are attacking..make it fail.
Cruise missiles and other "Standoff launch" munitions enable an attacker to launch with a high numeric reality set against a defensive grid..as the launch platform is not engaged..and may be re-armed or re-positoned for next strike.
The next factor is the numbers of munitions sent arriving at target co-ordinates.
The munition may fly by stealth or penetrate thru sheer speed.
Both realities now exist with Cruise missiles....both the U.S. and the Russians have this capability.
High arc trajectories of ICBM's provide several weaknesses by which they may be detected and destroyed in flight.
Low trajectory brings a higher success result...the only factor in low trajectory is gravity and fuel to obtain distance values needed for an attack on the Continental United States.
It is rumoured that the Russians have a cruise missile flight profile ICBM.
If true..this would yeild an advantage,as launch detection might not be noticed until its too late.
To meet this reality...a nation would need a detection grid like a dome....even then..what good would it do..if one did not have the means to aquire and target mulitple incomings below several hundered feet.
Discussed in think tank is the reality of a forward rocking ladder which would see an attacker blind his adversary in steps....in this case...nuclear detonation airburst to EMP a defence grid.
This is theoretical..as EMP also effects the attacker missiles and launch platforms in the process.
The design is to minimize first response and second strike by the defender.
Most important point****....the defender is responding to first stike..and arming for first response...all while his grid is in chaos.
The attacker has minutes to re-postion..evaluate first stike success..and adjust targeting.
To be blunt...the use of nuclear weapons would not factor moral concern.
The attacker could damage part of a defence grid...part of a nations info-structure[ie..cities]..and negotiate a term in view of damage sustained by the defender.
It would make no sense to Russia to really attack the U.S. to occupy it for whatever...the population would never submit...no advantage of exploiting resources could be obtained by Russia.
So in a real sense..if it ever occured..it would be for pure hate and spite...maybe over a dispute or envy.
During the 2nd WW....Russia sacrificed its population in order to overcome Nazi Germany.
The Germans simply could not kill or destory Soviet military assets at the rate they were being lost by the Germans.
Should the Russians ..or Chinese ever decide to attack America with Nuclear weapons.....the loss of millions of citizens and vast regions of territory would allready be conceeded.
With the second moral issue tossed aside..the reality now comes down to a sequence of historic events.
If Russia and China are desiring to do this to America...when would it happen?....and what could trigger such an insane descision?