Why are they supporting him? Probably because he favors returning US military personnel from bases on foreign soil, giving old enemies free reign around the globe.
Yeah! The Russkies could finally get their hands back on Afghanistan!
It worked so well for them the first time.
You are exactly, dead on, correct. Isolationist foreign policy gives Russia free reign to reconstruct the Soviet Union and gives China the opportunity to build their Chinese Empire. Simple enough.