President Donald Trump is pushing tariffs to force companies to move manufacturing to the United States. Almost half of all new cars are built somewhere else, and the supply chains for parts and materials are murky. But even the “most American-made” cars take at least 25% of their parts from other countries. So, how much can the industry reshore? How much more would a car cost if it had 80 percent US parts? 90%? CNBC dove in to find out.