Gov. Paul LePage left no doubt Wednesday that his proposal for a new two-year budget, scheduled for Friday, will have major changes in store for the state income tax.

“When the budget goes up on Friday,” he said in his inaugural address, “I will give you a hint, we’re going after the income tax.” (In a written version of the speech, LePage said, “We will start by getting rid of the estate tax and income tax on pensions.”)

LePage managed to cut income tax rates in his first year in office back in 2011, yet he reiterated his pledge Wednesday that he wants to eliminate the state income tax.

While LePage has plans for a significant tax cut in store, it’s the governor’s duty to present a responsible plan to account for the lost revenue that would inevitably result from an income tax cut.

The plan could include significant, money-saving structural reforms for state government. But LePage’s administration has said the coming two-year budget proposal will be about the same size as the last: about $6.3 billion. Without a major decrease on the spending side, then, a major income tax cut would leave significant ground to be made up in order to balance the state’s books.

Maine’s individual income tax, the state’s largest revenue source, netted $1.4 billion in the fiscal year that ended June 30, 2014.

LePage has suggested applying the state sales tax to a broader range of goods and services to compensate for some of the lost revenue. In order to make up a significant amount, though, the state would have to eliminate many politically popular sales tax exemptions. Indeed, eliminating exemptions on groceries, heating oil, amusements and a whole range of services — from haircuts to consultations with attorneys — could make up a substantial chunk of revenue. ( The Tax Foundation has calculated that the state’s exemptions total about $1.87 billion in forgone revenue annually.) But those also are changes laden with political minefields: special interests and industry groups can be counted on to fight to spare specific goods or services from taxation, as they have in the past.

If some popular exemptions stay on the books, then, making up the lost revenue through the sales tax could depend on raising the tax rate (which is scheduled to drop back to 5 percent on July 1 from the current 5.5 percent level). And that’s a move that LePage has vehemently opposed.

Given the politics — LePage’s own and the resistance that sales tax changes would encounter — LePage is setting the stage for a major political tussle that could throw basic budget math into question.

LePage need only look to a fellow Republican governor, Sam Brownback of Kansas, for a cautionary tale of an irresponsibly ambitious income tax-slashing proposal without a plan to make up for lost revenue. (On a smaller scale, LePage’s first-term tax cuts weren’t paid for with major spending cuts or tax changes. The result was about $350 million less in revenue to fund the state budget in effect until June 30, forcing the governor to propose eliminating municipal revenue sharing and property tax relief programs to make up for the lost revenue.)

Brownback signed ambitious income tax cuts into law in 2012 and 2013 that lowered the top individual income tax rates to 4.8 percent from 6.45 percent. Under the law, the top rate will continue to drop and inch closer to zero if the state has sufficient revenue. Significantly, the plan also effectively exempts nearly 200,000 businesses and their owners from paying any income taxes because Kansas shields “pass-through income” from taxes — that’s business income that owners report on their individual tax returns.

The result? Just days after Brownback was narrowly re-elected in November, budget officials revealed that state revenues had underperformed projections by $279 million for the current fiscal year — which the state will have to make up through difficult budget cuts (the Kansas Supreme Court has already ruled that the state’s school funding levels are unconstitutional) and by spending virtually all of the state’s reserves. The situation has led ratings agencies to downgrade Kansas’ credit ratings.

And the tax cuts haven’t proved the economic spark proponents were hoping they would be. Job growth in Kansas lags the national average — and it lags job growth in surrounding states with higher tax rates.

Republican governors across the country are taking note of Brownback’s experience and, in some cases, reining in their tax-cutting ambitions. As LePage pushes major income tax-slashing plans this winter, he’d best follow the lead of those Republican governor colleagues. Above all, LePage owes voters fiscal responsibility.

The BDN Editorial Board

The Bangor Daily News editorial board members are Publisher Richard J. Warren, Editorial Page Editor Susan Young, Assistant Editorial Page Editor Matt Junker and BDN President Todd Benoit. Young has worked...