Believe it or not, betting markets now rate Pete Buttigieg, the 37-year-old mayor of South Bend, Ind., in the top-tier of Democratic presidential candidates. He has about a 10% chance of winning the party’s nomination—right behind Joe Biden, and well ahead of Sens. Elizabeth Warren, Cory Booker and Amy Klobuchar. His rise is a testament to changing American politics as well as his skill in packaging progressive policies and methods in a smooth, moderate persona.

Presidential politics has long been entrepreneurial, but it’s...