But in 1935, after a New York City slaughterhouse operator was convicted of violating the poultry code, the Supreme Court called into question the whole approach of the New Deal, by holding that the N.I.R.A. was an “unconstitutional delegation by Congress of a legislative power.” Only Congress can create rules like the poultry code, the justices said. Because Congress did not define “fair competition,” leaving the rule-making to the president, the N.I.R.A. violated the Constitution’s separation of powers.

The court’s ruling in Schechter Poultry Corp. v. the United States, along with another case decided the same year, are the only instances in which the Supreme Court has ever struck down a federal statute based on this rationale, known as the “nondelegation doctrine.” Schechter Poultry’s stand against executive-branch rule-making proved to be a legal dead end, and for good reason. As the court has recognized over and over, before and since 1935, Congress is a cumbersome body that moves slowly in the best of times, while the economy is an incredibly dynamic system. For the sake of business as well as labor, the updating of regulations can’t wait for Congress to give highly specific and detailed directions.

The New Deal filled the gap by giving policy-making authority to agencies, including the Securities and Exchange Commission, which protects investors, and the National Labor Relations Board, which oversees collective bargaining between unions and employers. Later came other agencies, including the Environmental Protection Agency, the Occupational Safety and Health Administration (which regulates workplace safety) and the Department of Homeland Security. Still other agencies regulate the broadcast spectrum, keep the national parks open, help farmers and assist Americans who are overseas. Administrative agencies coordinated the response to Sept. 11, kept the Ebola outbreak in check and were instrumental to ending the last financial crisis. They regulate the safety of food, drugs, airplanes and nuclear power plants. The administrative state isn’t optional in our complex society. It’s indispensable.

But if the regulatory power of this arm of government is necessary, it also poses a risk that federal agencies, with their large bureaucracies and potential ties to lobbyists, could abuse their power. Congress sought to address that concern in 1946, by passing the Administrative Procedure Act, which ensured a role for the judiciary in overseeing rule-making by agencies.

The system worked well enough for decades, but questions arose when Ronald Reagan came to power promising to deregulate. His E.P.A. sought to weaken a rule, issued by the Carter administration, which called for regulating “stationary sources” of air pollution — a broad wording that is open to interpretation. When President Reagan’s E.P.A. narrowed the definition of what counted as a “stationary source” to allow plants to emit more pollutants, an environmental group challenged the agency. The Supreme Court held in 1984 in Chevron v. Natural Resources Defense Council that the E.P.A. (and any agency) could determine the meaning of an ambiguous term in the law. The rule came to be known as Chevron deference: When Congress uses ambiguous language in a statute, courts must defer to an agency’s reasonable interpretation of what the words mean.