Basically by pushing Ukraine into joining NATO Ukraine becomes a major security risk for Russia. (Russian cities are now in shelling range of NATO weapons). He is realist brained so he also said Washington should prevent Moscow from allying with Beijing but even that isnt hawkish enough for libs.
Theres a plenty of reactions but this article is one of example of :LIB: reaction. Gems include stating that he is wrong because he treats democracies and dictatorships the same in geopolitics, as if the US need votes to put their troops all over the world lmao.