Brazil, the embattled South American nation that has seen its fortunes rise and fall dramatically in the past few years, is once again looking like a country that foreshadows major global trends. This time, it is flashing warning signs about the coming battles in the worldwide campaign against corruption.

For the past few years, Brazil has been in the news for its successes in rooting out embezzlement and bribery schemes involving the country’s industrial giants and its political class. But last week, Brazil’s corruption-plagued Chamber of Deputies took a controversial late-night vote. Rewriting an anti-corruption bill into one that would do the opposite of what it originally intended, they made it possible to sue and imprison judges and prosecutors for abuses of power. They also removed the legal definition of what constitutes unlawful enrichment and a clause that sets out protections for whistle-blowers. With that, the legislators signaled their resolve to thwart anti-graft efforts. ...