Article 5 of the NATO treaty, i.e., an attack against one is an attack against all. How many Americans want to die for Lithuania?
How many Russians want to die over Lithuania?
The EU put the sanctions on. If Russia attacks Lithuania over it, the US will be obligated and all of NATO will be obligated to enter the war.
I don’t think Russia will do squat. They are already bogged down in Ukraine. There are ethnic sections of Russia ready to rebel. Oh Russia will cut oil off to Lithuania, but Lithuania already said they were prepared to go without Russian oil and it wouldn’t cause any critical problems for them.