Hard cases make bad law, says the courtroom adage. And sometimes, foolhardy disputes make the hardest cases.

The Minnesota Supreme Court is face to face once again with a difficult case created in a largely frivolous feud. The case threatens not only to make bad law but to dent the court's own institutional reputation.

The Minnesota Senate, et al., vs. Mark Dayton is back in the court's lap after the predictable failure late last month of court-ordered mediation aimed at forging agreement between the state's DFL governor and Republican legislative leaders.

Again the court is challenged to pass judgment on an implausible power play by Minnesota's frustrated governor — who happens to have appointed four of the six justices who must make the decision.

If they invalidate as unconstitutional Dayton's strong-arm veto of legislative funding at the end of this year's budgetmaking session, the justices might cloud the governor's legacy near the end of his long political career.

But allowing Dayton's veto of the Legislature's operating appropriation to stand — even though it was issued, not because Dayton objected to that spending itself, but expressly to "force" lawmakers to yield to the governor's wishes on other policies — might legitimize a wholly dysfunctional level of institutional total war among the branches of state government.

Worse, depending on how the justices lined up — whether they split along partisan fissures — the case could deliver another hit to already shaky public confidence in the true impartiality of courts.

The court got into this fine mess after both GOP legislative leaders and Dayton fought their usual ill-tempered budget battle with procedural "gotcha" tactics even more underhanded than usual. Dayton sprang the last surprise last spring, when he used his "line-item veto" power to block the new budget's operational funding for the by-then adjourned House and Senate. He insisted they agree to renegotiate tax bill provisions Dayton abhorred but had reluctantly signed into law. The GOP had attached a "poison pill" provision that would have defunded the Revenue Department had Dayton vetoed the tax measure.

By last month, the spectacle was before the high court, which was asked to decide whether a lower court was right in rejecting Dayton's creative use of the line-item power as improper. Wanting no part of the thankless task, the court got creative itself.

In a Sept. 8 order, the justices managed to issue a unanimous nondecision that sent the squabbling parties back to try again for an agreement. The court held that the governor did indeed have the "power" to line-item veto the legislative appropriation, but added that a "constitutional power may not be used to accomplish an unconstitutional result." It reserved judgment on whether imperiling the funding of an independent branch of government would be such a forbidden result under the separation of powers doctrine. And it asked for more information about just how long the Legislature could keep functioning on leftover moneys.

All of which, of course, left everything more unsettled than ever.

The question before the court is not a simple one. The line-item veto is an unusual power. Most state constitutions have it; the federal Constitution does not. The governor's power to reject individual spending items — but only individual spending items — while approving of the rest of a bill, was added to Minnesota's basic charter way back in 1876. But it was hardly ever used until the last quarter century. It's become popular in our era of divided government and partisan polarization.

A few governors have tried to get creative with the line-item power — using it to veto reductions in spending or to change policy. But Dayton, who likes most spending provisions he meets, had used the power lightly until this year.

Now he has set a whole new standard for inventive vetoing.

Earlier high court rulings have declared that the line-item veto, being an "exception" to normal constitutional structure, must be "narrowly construed to prevent an unwarranted usurpation by the executive of powers granted the legislature …"

For those who remember their civics, the usurping thing is that a line-item veto, even in its usual uses, allows a governor to cause a bill to become law even though that exact legislative text, as "edited" by the governor, was never approved by the Legislature.

But if anything truly qualifies as an "unwarranted" invasion of a legislature's independence, it would seem to be backing a demand for a particular act of legislation with a veto that threatens the lawmaking branch's basic funding.

Dayton has been publicly outraged to learn that, as it turns out, the Legislature may be able to access enough existing funds — rooting around underneath the equivalent of Capitol sofa cushions — to stay in operation all the way to next year's session. At that point political chaos may be in store if this dispute hasn't been resolved. But why Dayton feels so misused by the lawmakers' warnings that they might go broke before the session is a bit mysterious.

Wasn't it his intention all along to cause them money trouble, or anyhow money worries? In a commentary on these pages last week, Dayton wrote that "the reason for my veto was to try to force them to revise their 2017 tax bill …"

To "force" them. You "force" people to do things by applying pressure. While GOP lawmakers contributed to the bitter end of the session — and whatever one thinks of the underlying tax policy disputes — legislative leaders owed it to their institution's independence to make the fuss they have about this attempted intimidation.

And so, it's up to the court. Last week the justices, still hesitant to make a decision, ordered up still more precise information about just how much loose change the Legislature can find — just how long the besieged legislative city can hold out. The court may be tempted to seek a way of washing its hands of this mess once again, if the Legislature can last long enough to take up its own defense in February.

But the justices would serve Minnesota better with a clear answer: Is one governmental branch using its powers to "force" obedience from another branch what the framers of our republic had in mind?

Clarification

The Minnesota Department of Human Services has objected to a recent column in which I criticized its Minnesota Sex Offender Program. On reflection, I can see that some of my language did overstate certain concerns about the program. MSOP does provide some periodic review of clients' progress in treatment, some individualization of treatment plans and some less-restrictive housing options.

D.J. Tice is at Doug.Tice@startribune.com.