I think the most important way to prevent the growth of Trumpism is for the mainstream media (which is progressive) to treat mainstream Americans (many of whom are more conservative than are coastal elites) more respectfully. This former NPR executive is very thoughtful regarding the manner in which the NPR agenda is set from a progressive perspective, https://nypost.com/2017/10/21/the-other-half-of-america-that-the-liberal-media-doesnt-cover/