Republican gubernatorial candidate Larry Hogan. (Joe Lamberti/AP)

LARRY HOGAN, the Republican candidate for governor in Maryland, dropped a policy bomb into the campaign the other day. Speaking at a retirement community along with his Democratic opponent, Lt. Gov. Anthony G. Brown, Mr. Hogan said that once he gets spending under control, his administration would “completely eliminate state income taxes for pensions and retirement income.”

Unsurprisingly, he elicited hearty applause from the retirees.

We’d like to report that, along with his blockbuster tax cut proposal, Mr. Hogan released detailed projections showing how much revenue it would cost the state and which programs he would target for commensurate spending reductions. But we can’t, because he didn’t.

Hey, said Mr. Hogan — it’s just an idea! “When we’re ready to make an announcement about it, we’ll have it all figured out, but tonight it’s just an aspiration of something we’d like to try to accomplish,” he said.

That slapdash remark fits a pattern in Mr. Hogan’s campaign. Whether it’s because he doesn’t really expect to win or because he simply can’t be bothered to think through and develop actual policies, his approach has cemented the impression that he is winging it on the campaign trail.

Mr. Hogan, like some first-time candidates for local county councils, is long on slogans but short on positions. He has issued no position papers, no detailed plans and no thought-out policies.

Mr. Brown has a platform replete with numbingly detailed policies, which voters are free to evaluate. By contrast, Mr. Hogan tends to improvise, as he did in proposing a massive tax cut for which he could supply no details about the fiscal impact on the state. As it turns out, Republican lawmakers proposed similar-sounding legislation this year — exempting retirement income, including pensions, 401(k)s and the like, from state income tax. According to an analysis by the General Assembly’s Department of Legislative Services, doing so would drain $1 billion from state coffers annually, plus another $600 million or more from local governments. The legislation went nowhere.

Given that Maryland’s annual general fund revenue is about $16 billion, Mr. Hogan’s proposed cut would translate into a 6 percent reduction in state income. That means Annapolis would also have to slash spending by 6 percent — equal to what it cut from Maryland’s general fund at the height of the “Great Recession.” Would Mr. Hogan lay off state workers? Impose furloughs? Slash spending on social services? Public safety? Public schools? Higher education?

He isn’t saying. Instead, he insists that Maryland can painlessly reduce spending by eliminating unspecified “waste, fraud and abuse” — the emptiest cliche in American politics.

Mr. Hogan’s campaign has criticized the administration of Gov. Martin O’Malley (D) — and by extension, Mr. Brown — as tax-and-spend liberals who are hostile to business. That’s a fair critique if Mr. Hogan can furnish a plausible alternative. He hasn’t.

Instead, his aversion to detail, or anything resembling empirical evidence that would buttress a legislative program, has produced a campaign that lacks credibility. If Mr. Hogan is not bothering to mount a serious campaign, then why should Maryland voters take him seriously?