President-elect Donald Trump is now aiming his Twitter feed at General Motors over cars that the company makes in Mexico. Trump says GM should make the compact Chevy Cruze model in the U.S. or risking paying a “big border tax.” 

General Motors and the number two U.S. automaker have both faced Trump’s ire for overseas manufacturing. But these are also international companies, and there’s a very real economic reason why these companies want to build cars abroad.

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