Trump is wrong about trade because he sees it through the eyes of a businessman, not an economist. A successful businessman knows that he must always work to maximize his profits, and he can do that only if the goods and services he provides bring in more money than he spends in their production. Trump incorrectly compares a business to an economy when he suggests we "win" if we export more than we import. That's what mercantilism was all about: maximizing net exports. But whereas maximizing net sales is best for a business, it's not best for an economy.
As Don Boudreaux points out, an economy is not a business. "The ultimate goal of economic activity is consumption," whereas the ultimate goal of a business is to generate profits.
As a businessman, Donald Trump understands what ails the economy: taxes are too high, and regulations are too abundant. He's absolutely right when he says that "we tax and regulate and restrict our companies to death." If he becomes president and cuts and simplifies taxes and reduces regulatory burdens, then the economy will surely boom. But if he raises tariffs on "cheap" imports he will only succeed in impoverishing us all. Buying cheap things from other countries allows us to spend more on other things that enrich our lives.
Trump is wrong when he complains that we allow other countries to export to us tax-free, and that as a result "we have become more dependent on other countries than ever before." Trade allows people to specialize in what they do best. Every person and every business in the world is totally dependent on other people and other businesses; no single person or business can produce more than a tiny fraction of what is needed to survive in today's complex and dynamic world. There's nothing wrong with being dependent on other people, other businesses, and other countries. Being dependent on others is a basic fact of life in the modern world. It's not something to reject, it's something to celebrate, for otherwise we could not enjoy the highest standard of living in the history of mankind. Maximizing net exports would weaken, not strengthen our economy.
Trump is arguably a smart and successful businessman, but that doesn't mean he understands how an economy works.