Former President Donald Trump was ridiculed Friday after his former adviser admitted he “could not get his head around” a basic fact. Former adviser Fiona Hill reports in a new book reviewed by the Guardian that Trump, as president, had a hard time understanding Ukraine was a country. “Trump made it very clear that he thought, you know, that Ukraine, and certainly Crimea, must be part of Russia,” Hill reportedly said. “He really could not get his head around the idea that Ukraine was an independent state.” Hill, who served on the U.S. national security council from 2017 to 2019, reportedly mad…