Not a surprise at all, there we go:
Trump orders the deployment of 'two nuclear submarines' in response to 'highly provocative' comments from Russia
Said the frying pan to the saucepan: move out of the way, you're getting me dirty.
This was the latest post from Medvedev at X that he got on Trump's nerves, 28 July.

Then Trump

Then Medvedev on TG, 31 July

From RT article above, it mentions about Medvedev post:
The latter remark referred to the legendary ‘Perimetr’ system, dating back to the Soviet era and presumed to still exist in Russia. The autonomous system is believed to be an apocalyptic dead man’s switch, capable of firing the surviving nuclear arsenal at once in a scenario where the country was hit by a devastating first strike that eliminates its leadership and breaks the chain of command responsible for ordering retaliation.