If Donald Trump were to become president, he would not be able to start a trade war with China, said Gordon Chang, author of "The Coming Collapse of China." That's because the Chinese have already been targeting American businesses, he said Friday.

In Thursday night's Republican presidential debate, Trump clarified his call for a 45 percent tariff on Chinese goods. "The 45 percent is a threat that if they don't behave, if they don't follow the rules and regulations so that we can have it equal on both sides, we will tax you."