I seriously doubt it. You have to be absolutely bonkers to start nuclear war over one person. Russia is insane but not suicidal.
Now the escalation ball's on our court. Are you willing to die for Latvia?
(And Medvedev does appear to be that bonkers)
Trump would almost certainly not intervene with nukes to protect non-US soil if Russia launched first, but there are plenty of European countries with nukes. Anyone in charge of Russia would have to accept the possibility that a first strike would leave them with a bad time.