On July 25, 2013, a high-ranking federal law enforcement officer took a public stand against malfeasance on Wall Street. Preet Bharara, then the United States attorney for the Southern District of New York, held a news conference to announce one of the largest Wall Street criminal cases the American justice system had ever seen.

Mr. Bharara’s office had just indicted the multibillion-dollar hedge fund firm SAC Capital Advisors, charging it with wire fraud and insider trading. Standing before a row of television cameras, Mr. Bharara described the case in momentous terms, saying that it involved illegal trading that was “substantial, pervasive and on a scale without precedent in the history of hedge funds.” His legal action that day, he assured the public, would send a strong message to the financial industry that cheating was not acceptable and that prosecutors and regulators would take swift action when behavior crossed the line.

Steven A. Cohen, the founder of SAC and one of the world’s wealthiest men, was never criminally charged, but his company would end up paying $1.8 billion in civil and criminal fines, one of the largest settlements of its kind. He denied any culpability, but his reputation was still badly — some might argue irreparably — damaged. Eight of his former employees were charged by the government, and six pleaded guilty (a few later had their convictions or guilty pleas dismissed). Mr. Cohen was required to shut his fund down and was prohibited from managing outside investors’ money until 2018.

Now, with the prohibition having expired in December, Mr. Cohen has been raising money from investors and is set to start a new hedge fund. He’ll find himself in an environment very different from the one he last operated in. His resurrection arrives as Wall Street regulation is under assault and financiers are directing tax policy and other aspects of the economy — often to the benefit of their own industry. Mr. Cohen is a powerful symbol of Wall Street’s resurgence under President Trump.