The goal of the tariffs is to make Chinese produced products less competitive against American produced products. For instance you sell widgets. You can take advantage of abysmal labor conditions in China to have these widgets manufactured and produced for $70 there. Or you can have them produced in America by laborers who work in much more pleasant conditions and are legally obligated to higher wages for $100. For a company that's just interested in maximizing their bottom line, it's not much of a decision. But then imagine tariffs suddenly mean the costs become comparable. Now you have a strong economic incentive to use American labor.

Completely free trade sounds great on paper, but in reality it basically just ends up rewarding the lowest common denominators of the world in labor conditions. $1000 iPhones are produced in factories in China where each worker earns several dollars per day and live in on-site dormitories literally surrounded by so-called 'suicide nets' to try to deter impulsive suicides caused from both living and working in such conditions. In the US we'd never accept such conditions, yet in the process of trying to improve the standard of labor in the US we ended up causing companies to simply fire their American workers, and then shift all their labor overseas -- sending trillions of dollars in incentives to the countries with the worst labor standards on this planet. That this hasn't been as much of a political issue to now emphasizes how much both parties in establishment politics are indentured to corporate interests.