The grand myth of modern Republican politics — the trickle-down theory that sweeping tax cuts generate rising revenues — has come crashing down in Kansas.

An exuberant Gov. Sam Brownback enacted the largest tax cuts in the state’s history in 2012 and 2013, a $1.1 billion upper-bracket boon for which he promised rich economic returns. But the governor and the Republican Legislature were soon shortchanging the state’s public school budgets in compensation.

Per-pupil state aid has declined from $4,400 to $3,800 during the Brownback years. That has forced reductions in staffing, classes and school days in the more poorly financed districts. It has also fueled the current crisis in which the public school system faces a shutdown on July 1, imposed by the State Supreme Court, unless the state government restores some of the equity it sacrificed in pursuing the trickle-down myth.

Even some Republican supporters of Mr. Brownback, finding their schoolchildren threatened by declining standards, are calling for the reversal of some of the tax cuts. They shouldn’t expect a positive response. The governor and the Legislature have rebuffed and evaded rulings from the State Supreme Court, which found that the Legislature had violated the State Constitution’s clear requirement that it provide fair and adequate support for all school districts, including impoverished ones with less property tax revenues.