The U.S. Supreme Court's decision this week to let stand the lower court ruling in the unsung case of Clayton vs. Niska didn't make any headlines. But for those of us who believe in a robust debate under the First Amendment, the implications are unsettling.

Bonn Clayton, active in Republican Party politics in Minnesota, "distributed campaign material falsely indicating that the Republican Party of Minnesota endorsed three candidates for the Minnesota Supreme Court in the November 2012 election," according to a state appellate court. The party endorsed no candidates that year, but Clayton, "despite knowing the convention's decision … sent an e-mail to roughly 7,000 state Republicans on October 18, 2012, promoting a website, judgeourjudgesmn.org, that implied a different result."

Clayton was fined by an administrative panel whose members concluded that he'd violated a state statute barring any "person or candidate" from making "a false claim stating or implying that a candidate or ballot question has the support or endorsement of a major political party or party unit or of an organization" and from stating "in written campaign material that the candidate or ballot question has the support or endorsement of an individual without first getting written permission from the individual to do so."

A state court upheld the ruling in relevant part and, on Monday, the Supreme Court declined to hear Clayton's appeal.

Given the court's reading of the facts, Clayton's violation of the statute seems clear. His lawyers argued in the Minnesota Court of Appeals that the statute violates the First Amendment. They lost. They petitioned the U.S. Supreme Court to hear their challenge, but the justices declined.

Why does the case matter? None of us, presumably, are greatly sympathetic to liars. But the problem isn't that Clayton lied. The problem is that he was fined by a state agency for lying. And as a plurality of the Supreme Court reminded us recently in United States vs. Alvarez — the "Stolen Valor" case — the First Amendment does not allow the government to punish speech merely because it is false: "Were the Court to hold that the interest in truthful discourse alone is sufficient to sustain a ban on speech, absent any evidence that the speech was used to gain a material advantage, it would give government a broad censorial power unprecedented in this Court's cases or in our constitutional tradition." Therefore the state, to regulate even false speech, must narrowly tailor its statutes to serve the compelling interest of preventing a serious harm.

The Minnesota court, perfectly aware of this tradition, concluded that "avoiding false speech that misleads the public regarding elections is a compelling interest" — and that the statute in question is narrowly tailored to serve that end. And the U.S. Supreme Court saw nothing in this judgment worth reviewing.

But for those of us in the dwindling tribe of free speech near-absolutists, there's reason to be fearful. The Minnesota court tried to limit the potential reach of the statute by making clear that it applies only to those who knowingly propound false endorsement claims: mere carelessness or error wouldn't be a violation. The difficulty is that once the state is allowed to regulate speech that misleads the public during an election campaign, there's no logical reason to stop at endorsements.

Imagine, for example, a statute punishing any "person or candidate" who makes "a false claim stating or implying that a candidate has taken a position that he or she has not." Such a law certainly would serve the same compelling end of "avoiding false speech that misleads the public regarding elections." It would also put the government in the position of potentially scrutinizing every advertisement by every campaign, every speech by every candidate, every social media post by every voter. At election time, falsehoods will likely be found lurking in all of the above.

Such a statute would apply even were the lie repeated in casual conversation — as long as the speaker knew it to be false. If the state has the power to prohibit false claims about who's endorsed a candidate, it's hard to see why the state can't also prohibit false claims about anything else that might mislead the public at election time.

Of course, one might reply that the government is reasonable, that it would never take things so far. There is little in history, however, to suggest that official powers, once approved, will be limited to some narrow realm where we don't mind their application. On the contrary, regulatory authority, once planted, tends to grow. It's hard to think of any government agency that has ever said, "We've done enough. Let's stop for a few years."

To be sure, given the adolescent quality of most campaign discourse these days, it's tempting to wish for a magic bullet to make the nonsense stop. But the First Amendment exists precisely to temper that wish. The old constitutional truism, repeated by the Supreme Court in Alvarez, remains true: The cure for bad speech is good speech. In the heat of a political campaign, people are bound to lie. That's a terrible thing, and it does terrible harm to democracy. But letting the government regulate political speech is worse.

It's worth noting that the same laundry list, right down to those who make false posts on social media, would also be covered by the Minnesota statute involved in Clayton vs. Niska. Some legal scholars have suggested that the Supreme Court's decisions upholding campaign finance laws might also provide a ground for regulating false campaign speech. Others have argued that false speech should have little if any constitutional protection. Neither view is in the mainstream but each is provocative and interesting.