Because it would (hopefully) prove to Trump's supporters that his policies are in fact going to be hurting America's economy, and quite the opposite of "Making

Because it would (hopefully) prove to Trump's supporters that his policies are in fact going to be hurting America's economy, and quite the opposite of "Making America Great Again". Once local shopkeepers, business owners and workers realise that the 'brain drain' caused by these policies, as well as the lack of tourists spending dollars in their establishments etc. is causing actual pain to their hip pockets, then they may realise that being a part of the global community may be a good thing, and the isolationist policies not so much. By the same token, I would ask you how US imposed economic sanctions on other countries are expected to work to depose the leader of those said countries? Sanctions usually affect the general population who usually have nothing to do with their leader's actions. We end up with children and other innocents dying from starvation or disease while the regime continues unabated. The different with the US is that (hopefully), the people can have sway over the President's actions, and take action themselves to effect change.