Liz Truss won the job of British Prime Minister Monday, and now we’ll see if she can lift her Conservative Party and country out of the economic and energy mess into which Prime Minister Boris Johnson has driven it.

Ms. Truss defeated rival former Chancellor Rishi Sunak 57%-43% by rallying the rank and file behind her with a Thatcherite economic message the party and U.K. haven’t heard from the Conservatives in years. Tax cuts top her agenda, including a reversal of Mr. Johnson’s 2.5-percentage-point payroll-tax increase and planned increase in the corporate tax rate to 26% from 19%.