With polls suggesting that Kamala Harris has at least a 50% chance of winning next month’s US presidential election, questions about her economic-policy agenda have come to the fore. Of course, much will also depend on down-ballot outcomes. If the Democrats were to win the White House and both houses of Congress, they could implement fiscal policies with a simple majority (through the so-called budget-reconciliation process). Otherwise, a Harris administration obviously would be more constrained.

When Harris (briefly) ran for president in 2019, her economic proposals were well to the...