Would make Iraq and Afghanistan look like child's play. Border states would be dragged into the chaos very quickly. Europe would simultaneously be supporting Canada like we are in Ukraine, while trying to destroy the US economy with sanctions etc. Good luck USA

If we can't deter US from taking Greenland then we definitely can't deter Russia from invading the Baltics. On the other hand if we show that we are ready to fight US over Greenland then Russia will have to assume we would defend the Baltics.