Are you serious?
“contaminate much of the country?” They have planes, missiles, would not wait until they got that close. Israel can hit Moscow.
Yes, I am serious. Invading armies would be too spread out at a distance for the nukes to have the desired effect. Once they are massed in the border area they can be taken out hundreds of thousands at a time, but at great risk of contamination.
Decapitating the leadership is an option, if you can find them. They certainly won't be sitting in HQ in their capitol city or a military base waiting to be vaporized!