Sometime during the 90s, Russia attained nuclear superiority over the U.S. While Russia's large, strategic nuclear weapons have remained in parity with the U.S., Russia's tactical nuclear arsenal has been estimated to include between 20,000 to 40,000 weapons.
The former USSR achieved nuclear superiority during the 1980s, and after the disintegration of the USSR, Russia managed to maintain that superiority. The United States Armed Forces might be the most capable armed force in the world, but it lags behind Russia, when capability for conducting a nuclear attack is taken in to account.
The S-400 air-defense systems of Russia are capable of intercepting the LGM-30G Minuteman III ICBMs of the United States (which is the only American surface-to-surface missile capable of carrying a nuclear warhead). Also, the S-500, which is currently in development can intercept as many as 10 ballistic missiles at the same time.
And meanwhile, no American air-defense system is capable of intercepting the SS-18 Satan ICBM of Russia.