He was not a hurdle to be cleared easily. Brodsky had once spent about seven years suing Argentina for bond payments — and secured a lucrative settlement. (Addressing the United Nations in 2014, the president of Argentina accused hedge funds like Brodsky’s of “financial and economic terrorism.”) So while Brodsky held only a sliver of Puerto Rico’s debt — $379.5 million, according to court filings, or about 0.5 percent — he could, by deploying his skills in the legal system, punch above his weight in bankruptcy proceedings. One prominent lawyer who worked on the Puerto Rican debt crisis described Brodsky to me as “a very skillful adversary” who was also “a prophet of doom.” Jealous of his privacy, Brodsky rarely gives interviews and never releases any photographs of himself. During the Argentina proceedings, multiple news outlets published a head shot of a Captain Ahab-looking man — squinting eyes, white chin-strap beard — whom they identified as Brodsky. It was in fact a picture of the private-equity mogul Sam Zell. It is still the first Google Image result when you search for “Mark Brodsky Aurelius.” (Brodsky’s P.R. agents are aware of the mix-up but apparently see no reason to correct it.)

Though the rainy-day fund complaint was dismissed, Aurelius had another one in the works. Later in 2017, the fund was back in court with a separate clique of bondholders. This time, it plied a totally different method. Instead of firing around the edges, trying to pick off the budgets of the Boys & Girls Club and the ballet company, the firm aimed at the bull’s-eye: It leveled an argument that the bankruptcy process itself violated the U.S. Constitution. For the next two years, with this argument in hand, Aurelius scaled the federal appellate system. The District Court ruled against it, so it appealed; the First Circuit agreed on the merits but withheld a remedy, so it appealed again. Finally the case flopped onto the steps of the U.S. Supreme Court, which heard oral arguments in October and will issue a ruling before next August. If Aurelius wins, it will be one step closer to compelling Puerto Rico — a territory poorer than any state in the union — to pay the full $379.5 million that the firm most likely acquired at a steep discount.

The U.S. solicitor general, Noel J. Francisco, who wrote the federal government’s brief in the proceedings, has claimed that a victory for Aurelius would “undo years of progress toward Puerto Rico’s economic recovery, causing devastating practical consequences for the people of the island”; inflict “grave harm to innocent third parties”; and disrupt “billions of dollars” of financial transactions. Moreover, Francisco claims that the precedent set by a ruling in the firm’s favor could invalidate the election of the mayor of Washington and strip the governors of Guam and the Virgin Islands of their legitimacy. Aurelius holds that these are distractions from the core constitutional issue at hand. “The court should not be dissuaded by the opposing parties’ unfounded claims of ensuing ‘chaos,’ ” the firm said in a reply brief. “These claims boil down to an extraordinary assertion that the constitutional violation here is simply too blatant and too big to remedy.”

That a firm holding a paltry 0.5 percent of the island’s debt could trigger even one of Francisco’s hypothetical scenarios reveals the disproportionate power that this tiny corner of Wall Street has accrued over the past generation. Largely out of view, distressed-debt hedge funds have honed a set of tools for recovering bad foreign debt, turning courts into collection agents. The tools work so well, and with such sophistication, that it was probably a matter of time before they were requisitioned from abroad and applied to a territory of U.S. citizens.

Distressed-debt litigation was unimaginable for most of the history of modern finance. Private players like hedge funds stayed away from sovereign debt because there was no way for them to get their money back if a country defaulted; a hedge fund couldn’t take a country to court. During the twilight of the Cold War, the situation changed. The American government in 1976 passed a law that severely weakened the immunity of sovereign countries in U.S. courts; Britain followed with a similar law two years later. It happened almost entirely by accident: Officials, in trying to solve one problem, accidentally created a new one. What the officials had wanted to address was some trouble with state-owned enterprises like those in the Soviet Union. These enterprises behaved like private companies — maximizing their profits and in some cases expanding internationally — but because they were nominally organs of government, they were immune from litigation in international courts, giving them an unfair advantage over businesses in the West. To address the flaw, the U.S. and Britain passed laws allowing private enterprises to bring lawsuits against foreign governments in courts in, say, New York or London. Forty years later, the U.S.S.R. is long gone, but these laws are still on the books.