My guess is there's an economy of scale advantage when manufacturing large quantities in the US for the US market. The good news is some of the top game companies are in this top six, especially Wizards of the Coast and Pokemon. Around a third of my sales are products manufactured in the US. For some game stores it's much higher, considering how Magic (Wizards of the Coast) dominates. If prices do rise dramatically, it may mean a shut out for the smaller manufacturers who can't afford US production, meaning a consolidation and thinning of the herd. This makes a lot of assumptions, so maybe some publishers can comment on that.
If prices do go up and manufacturing continues abroad, the likely scenario for retailers is higher prices and more market erosion, with sales moving online. A $50 board game is expensive enough. Make it $60 and a portion of our customer bases will break off in search of cheaper options. Perhaps publishers will respond with more economical games, either lower quality parts or less content.
This tariff is all speculation, since this is being debated at great length. It's also unclear if a "pass through" tax reduction would follow. That would help someone like me, as I make a good portion of my income on my S-Corp profits, but most small retailers make their income via their salaries. That is, if they make any income at all. So like all things proposed with corporate taxes, the more money you earn, the more the proposed legislation helps you. Personally, I like a steady, even playing field without the massive disruption these schemes entail.