It's easy to get into Russia. It's hard to get out.
As for most of the Jews being killed later in the war, that's partly because most of the victims were in territories the Germans had to conquer and stabilize first. And it's preposterous to assert that Hitler threw millions of his best troops and other resources into Russia just to intimidate the Brits. Buchanan has it backwards; going into Russia doomed any chance Hitler had of defeating Britain.
I have to wonder if Buchanan is partly motivated by the hatred of England which simmers within some Irish Catholics.