Alongside his promise of 25 million jobs, Trump has also said he can get America growing at 4% a year again. That would be almost double what Obama achieved. The U.S. hasn't seen consistent 4% economic growth since the tech boom of the late 1990s.
Of course they matter. Trade deficits arise when we import more than we export. Easy said. It's a tad bit more complicated. When we keep incurring these deficits, year after year, we use our domestic currency (the $) to pay for those imports. This results in our trade partners getting a considerable supply of those $.
Why does the U.S. have such a large trade deficit with China? Prices of consumer goods in the United States have been remarkably low and stable for decades. One of the most important reasons for this, besides sound monetary policies conducted by the Fed, is international trade with developing countries, such as China.