Edit: Great discussions and questions in the comments. Thank you all for keeping this article informative!
It doesn’t work that way. If Russia were to launch their ICBMs, the US would know through their satellites and would respond with their Minuteman III ICBMs and Trident SLBMs. From there, shit goes downhill really fast. If either nation were to deploy their nukes, the other would respond in kind. Besides, it’s not like RS-28 is some super powerful Gigaton warhead that would secretly travel across the atmosphere and wipe out the entire nation. The fact is, the US will detect a nuclear launch from Russia or any other nuclear state that they monitor.
Satellite used in Defense Support Program (DSP) to detect nuclear launches.
The days of one massive 20 Megaton warhead are obsolete. Modern ICBMs carry a system called MIRVs (Multiple Independent Re-entry Vehicles) which use 500 Kiloton – 1.5 Megaton warheads And still getting smaller. It’s more efficient to spread out the firepower to hit multiple cities with just 1 ICBM. This is how both Russian and American weapon systems currently work, but are being modified again under newer programs.
Due to the Strategic Arms Reduction Treaty (START) ICBMs and SLBMs have had the amount of warheads reduced down to one MIRV warhead in the nose cones, though not all of them have been converted at this time.
Edit: See Will Coleman’s comment below for an article that explains the reduction in MIRVs and other details about START.
Edit: Take a look at the comment below from Jonathan Stern, he attached an article explaining how the Minuteman III modernization program is fine tuning the targeting systems of these weapons to reduce CEP (Circular Error of Probability) to pinpoint detonations over small targets such as a missile silo. Advancements such as these reduce the need for larger yield warheads and the amount actual warheads required to perform a mission.
MIRV (each cone is a warhead)
That one shown is from the Peacekeeper LGM-118 (retired by 2005)
The Minuteman III and Trident II are the current deployed weapon systems in the US arsenal, but both are having their targeting systems updated to reduce the need of a larger yield warhead for effect and to reduce the need for multiple warheads to meet the START II treaty.
The bottom line, Russia is not the only nation that has upped their nuclear capability, the US has been actively modernizing their arsenal to meet and neutralize any threats.
Edit: This was originally written in early February, based off of assumptions that the current powers that held nukes are “rational actors” on the world stage. However, based on current events (Invasion of Ukraine), Mr. Putin’s delusions of reinstating the former Soviet Union’s sphere of influence have proven that he no longer fits in the category of “rational.”
Edit: There has been a lot of revising to this answer based off of all the great feedback that I have been receiving. I never thought that this answer would get so much traction weeks ago when I just gave a quick five minute reply. But the world has changed significantly in February 2022 and this topic is now very hot. With help in the comments I’m providing more details.