It's the old "laboratories of democracy" concept popularized by U.S. Supreme Court Justice Louis Brandeis in New State Ice Co. v. Liebmann to describe how a "state may, if its citizens choose, serve as a laboratory; and try novel social and economic experiments without risk to the rest of the country."
And by the way... Denmark is actually far less socialist than is purported by our Social Democrats and is, in fact, rapidly de-socializing.
Link: https://www.youtube.com/watch?v=tzEPKrHalaY&feature=youtu.be&fbclid=IwAR3cZbR8ShzfjbY4WfBaYEenh-wvNPhsLVRX_uDpq8PiTDaW5r6ZwhnT-vk