Scrutinizing the avuncular sphinx Chief Justice John Roberts throughout the impeachment trial of President Trump, I kept wondering whether he will preserve or ransack the legacy of the framers we revere — framers like the Republican Betty Babcock and the Democrat Dorothy Eck. It’s the question on all Americans’ minds: Do Mr. Roberts and his eight co-workers fully appreciate the public-spirited grandeur of the winter of 1971-72, when 100 Montanans, including housewives, ministers, a veterinarian and a beekeeper, gathered at the state capital, Helena, for the constitutional convention, affectionately nicknamed the “Con Con”?

The question haunts the current Supreme Court case Espinoza v. Montana Department of Revenue. This newspaper has called the dispute over whether state tax credits can apply to donations for scholarships to private religious schools “a proxy battle over school choice.” However, the back story is so clumsily specific to Montana’s small population and immense geography that the case doesn’t entirely translate to states where people outnumber cows.

The novelist Ivan Doig wrote that in the scruffy Montana of yore, “when you met up with someone apt to give you trouble from his knuckles, the automatic evaluation was ‘too much Butte in him.’” When, as the grateful graduate of a Montana public school, I was determining whether I had a duty to stick up for the Con Con framers regarding the Espinoza case, I spotted a sequence in the web address of an article about it in The Atlantic that read “montana-bigoted-laws.” At that moment this Bozeman girl had too much Butte in her. Dorothy Eck wrote no “bigoted” anti-Christian laws — she was a blatant Methodist!

Before it ended up at the Supreme Court, the Espinoza ruckus started with a $150 tax credit. Montanans will make an appellate-level stink about chump change because that’s the only available change. The tiny tax base is basically eight coal miners, a couple of ski lift operators, that family in Belgrade making organic goat cheese and Huey Lewis.

Kendra Espinoza counted on scholarships to help pay for her daughters’ tuition at Stillwater Christian, a private school in Kalispell. No wonder. At up to $8,620 per year, ninth grade is more than $1,000 higher than undergraduate tuition at the University of Montana. What we called a “band room” at Bozeman High, Stillwater considers a “conservatory.”

School choice partisans pounced when Ms. Espinoza and other private-school parents sued to overturn the State Supreme Court’s ruling that the tax credit for scholarship donations violated the “no-aid” clause for sectarian schools in the Montana Constitution. They argued that it was time to erase “antiquated” anti-Catholic laws against public funding for private religious education. The subtle former state senator Matthew Monforton denounced the law as “Jim Crow for Christians.”

It is worth pointing out that the eighth word of the ’72 Constitutionis “God.” In the first draft of the preamble, some wistful Jeffersonians tried to thank the “Spirit of the Creator” for “the quiet beauty of our state.” They were shot down in the Bill of Rights Committee because “not mentioning ‘God’ specifically would be unacceptable” and so they “voted unanimously to retain Him in the Preamble.” The framers included a priest from Great Falls, Mitt Romney’s cousin Miles, the self-proclaimed “first Roman Catholic ever elected to anything in Yellowstone County,” and enough Presbyterians to warrant their own photo op.

While the ’72 Constitution’s no-aid clause looks similar to its predecessor in the 1889 original, the update was motivated by fortifying public schools, not shunning people of faith. Rethinking education was, along with open government and the right to individual dignity, part of the Con Con’s crusade to take a stand that no one dared dream of at statehood: that Montana would be a state in a republic and not an exceedingly wide company town.

“We were known as the state that wore the copper collar, controlled by the Anaconda Company,” Ms. Eck once said. A swashbuckler for the League of Women Voters, she referred to the copper company lording over the “richest hill on earth” and thus the newspapers and politicians. “There were stories of how their lobbyists would sit in the balcony at the legislature and do thumbs up and thumbs down of how people should vote.”

The Con Con delegates, who arranged themselves not by party but alphabetically, were so preoccupied with the public interest that they agreed public funds could be spent only on public agencies. During deliberations on the no-aid clause, the pastor of Helena’s Plymouth Congregational led the charge of “preserving our public school system,” preaching, “that’s what this issue is all about. I don’t think we ought to dilute that in any way.” (Diluting that is the aim of Espinoza.)

Article X, Section 1, of the ’72 Constitution proclaims that it is the duty of the state to “develop the full educational potential of each person.” That is an expensive ideal in a desolate wasteland. Public schools are supposed to be a volume business, but tell that to the Great Plains. The state of Montana has about 60,000 fewer inhabitants than the number of students enrolled in New York City’s public school system. I have volunteered in that epic system, which is to say I have had to excuse myself from a struggling student to go cry in a bathroom, so I sympathize with an urban kid who might eye a parochial school as her best chance.

That school choice logic doesn’t apply to Montana, where the poorest schools often have the smallest class sizes. The Montana Free Press reported that out in Prairie County, “Terry High School’s sophomore class has just five students this school year.” Starting in first grade, my friend Genevieve would ride her horse Croppy to the Malmborg School near Bozeman Pass; one year she and her brother Pete were half the student body.

When USA Today asked Ms. Espinoza if she had any qualms about what her case could mean for public schools, she insisted, “They have plenty of money.”

How I wish that were true. Last year, the public school district in Kalispell announced $1.7 million in budget cuts, Great Falls recently lost almost a hundred teachers, and Billings just announced about $4 million in cuts that mean canceling fifth grade orchestra and band.

A Supreme Court decision on Espinoza is expected in June. If the justices rule against Montana’s voters, tax credits for private school scholarship donations could surge. Revenue that might revive the Billings fifth grade band program could underwrite the fifth grade band at a pricey Kalispell private school.

Kalispell is the seat of Flathead County, which between 2000 and 2015 added more than 15,000 jobs just as rural Choteau County was losing more than 300. Overturning the no-aid clause will shovel more money into the cities (where most of the private schools are) and kick Choteau while it’s down, thereby thwarting the framers’ plan to spare needy districts from taxing “their residents three or four times as much as rich districts to provide less than half as much money per student.”

The public schools the framers conjured ask the taxpayers to splurge on fairness, not privilege, to pull together, not away. That beekeeper, those clergymen and moms chartered a state in a republic where a first grader on horseback is supposed to be as big and important as the mountains. As the Supreme Court justices ponder whether to upend all that over what appears to be a $150 trifle, I’ll pass along this lesson of Montana winters: A collapsed roof starts with a single snowflake.

Sarah Vowell, a contributing Opinion writer, is the author of “The Wordy Shipmates” and “Lafayette in the Somewhat United States.”