Now that Donald Trump has criticized the “new calls to adopt socialism in this country,” Democrats and the media are already protesting that the socialist label doesn’t apply to them. But what are they afraid of—the label or their own ideas? The biggest political story of 2019 is that Democrats are embracing policies that include government control of ever-larger chunks of the private American economy.

Merriam-Webster defines socialism as “any of various economic and political theories advocating collective or governmental...