GOV. SAM BROWNBACK of Kansas says he has come to regret characterizing his policy agenda as a “real live experiment” that would test the efficacy of deep tax cuts to spur jobs and economic growth. In fact, Mr. Brownback’s choice of words was apt. Few if any governors have undertaken such an extreme trial-by-revenue-deprivation in a state so clearly lacking the economic means to withstand it.

Now, as the damaging social and budgetary impacts of his slash-and-burn fiscal measures have become apparent, Mr. Brownback, a conservative Republican seeking reelection this fall in a state where every statewide elected official is also a Republican, is in the disorienting position of trailing his Democratic challenger in the polls.

Mr. Brownback’s Kansas trial is rapidly becoming a cautionary tale for conservative governors elsewhere who have blithely peddled the theology of tax cuts as a painless panacea for sluggish growth. Most key indicators suggest that job creation and economic growth in Kansas are lagging those of its neighbors.

Mr. Brownback has cherry-picked the statistics to suggest that things aren’t as bad as they seem, while arguing that it’s still too early — more than a year and a half after his cuts were enacted — to gauge their full impact. Meanwhile, Wall Street’s bond rating agencies, taking note of plummeting tax revenue and a siphoning off of the state’s reserves to cover current and projected deficits, have weighed in with their own verdict: Moody’s cut Kansas’s credit rating last spring, and Standard & Poor’s followed suit last month.

“In our opinion,” S&P’s analysts wrote with lethal understatement, “there is reason to believe the budget is not structurally aligned.”

Yes, well, that is bound to happen when a state hacks personal income taxes, corporate taxes and sales taxes all at once without tapping an alternate source of revenue, or making commensurate cuts in spending.

As it happens, spending reductions have been sufficiently draconian and divisive that large numbers of Kansans, including more than 100 current and former GOP elected officials, have expressed alarm and are supporting the man trying to unseat Mr. Brownback, Paul Davis, the Democratic minority leader in the state’s House of Representatives. There have been particular expressions of anxiety about cuts to per-pupil expenditures in public schools, which have dropped more than 10 percent since 2008.

Other Republican-led states have embarked on tax-cutting programs. But few if any have done so without a fail-safe designed to protect essential state services, such as mechanisms that would abort tax cuts if revenue drops, or allow them only after revenue rises. In the special case of Texas, a combination of rising immigration rates and a robust oil and gas sector buffered the economy from the effects of tax cuts.

Kansas has no such innate advantages. To the contrary, non-partisan budget analysts for the state legislature project that without new sources of revenue or even deeper spending cuts, the state faces some $1.3 billion in deficits in the coming five years. That’s a big hill to climb in a state whose budget for general expenses is $6.3 billion.

Kansas is a politically conservative state, not a radical one; historically it has favored pragmatists like former senator Bob Dole, a Republican, and former governor Kathleen Sebelius, a Democrat. Mr. Brownback and his policies are a departure from that tradition. It’s possible he may recover from the predicament caused by his radical policy prescription. It’s unclear when Kansas will.