About a decade ago, the leaders of a Florida city held a closed-door meeting to discuss how to intimidate and silence a critic named Fane Lozman. So far, their plan has not worked.

Mr. Lozman calls himself “a persistent and tenacious underdog,” which may be an understatement. He is an indefatigable gadfly and an unusually successful litigant.

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“It’s not because I was going 60 miles an hour,” Chief Justice Roberts said, imaging what a driver might say. “It’s because of my bumper sticker.”

In urging the Supreme Court to hear the case, Pamela S. Karlan, a lawyer for Mr. Lozman, wrote that conflicts between the government and its critics were on the rise.

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“Recent years have seen a fresh surge of civic engagement, much of it involving criticism of the government,” she wrote. “Thus, the risk of retaliatory arrests remains a pressing concern.”