Elizabeth Warren has a plan — to annoy union members who work for state and local governments. With her “Medicare for All” plan, the top-tier Democratic contender is revealing a tension in the neo-progressive movement. Warren’s $20.5 trillion over a decade to pay for Medicare for All requires what she calls a “redirection” in funds: $6 trillion in “existing state- and local-government insurance spending.” Of this figure, $3.3 trillion goes for Medicaid, public insurance for poorer people. But the other $2.7 trillion comes from the funds state and local governments “currently spend on employer contributions to private insurance premiums for...