The rail portion of the Kerch bridge is rarely used these days. Only recently has Russia dared transport fuel across the bridge. It looks like an act of desperation. Ukraine has been increasing its reach into the Sea of Azov hitting what it can to diminish military supply to Russian forces in Crimea. So, not only has Russia had to pull back its Black Sea Fleet to Novorossiysk, its naval assets in the Sea of Azov are now at risk. What's a poor Putin to do? Find a safe harbor in Cuba, I guess.
Anyways, if this continues, Crimea would be the logical piece for Russia to have to let go. Ukraine has been hitting not only SAM systems but other radar, airfields, comms centers, supply ferrys, and command posts there. Now if they could just hit that bridge and put it OOC once and for all.
Russia is building new rail routes from Rostov-on-Don down along the coast to supply Crimea, but once other means of transport are sufficiently diminished, this lifeline will become a focal point for Ukraine. Oh, and I almost forgot, F-16s will start trickling in soon and with a lack of air cover, any remaining military assets in Crimea should be easy pickins'.
So this will hardly be the end of it, Russia will still have its meat wagons running poor soldiers into Donetsk, Luhansk, Kharkiv with guns at their backs. But losing Crimea will be not only a major miitary defeat for Putin but quite a blow to his self-esteem. And after all isn't that what this is all about?
With ATACMS, all things are possible.