President Trump’s contest against the deep state is moving into its final innings. It’s a multi-front dispute whose outcome could decide whether Mr. Trump — and future presidents — can, against resistance from Beltway bureaucrats, carry out their constitutional duty to take care that the laws be faithfully executed. Arguments Monday before the Supreme Court will test a president’s power to hire and fire leaders and directors of executive branch agencies.

Trump v. Slaughter centers on the president’s termination, without cause, of a commissioner of the Federal Trade Commission, Rebecca Slaughter. The commission, a consumer protection agency dating to 1914, was set up by Congress as a nominally nonpartisan agency. Its five commissioners serve seven-year terms, exceeding the duration of a president’s tenure. Congress decreed, too, that no more than three commissioners can be of the same party.

The commission’s creation, under a Democratic president, Woodrow Wilson, was a product of the Progressive era that sought to expand the federal government’s regulatory ambitions. Yet, like the Federal Reserve created in 1913, these administrative agencies blur the constitutional boundaries between the branches of government. In the case of the Fed, the Constitution assigns the monetary powers of the federal government to the Congress.

The FTC similarly blurs the separated powers by combining law enforcement — an executive branch power — with rule-making, which properly belongs to the legislature. Feature, say, the Biden-era FTC’s push to ban so-called non-compete clauses in employment contracts. What legal authority did the FTC have to intrude into private hiring decisions? The agency cited its mandate to prevent “unfair methods of competition.” 

That’s a stretch. No wonder, then, that courts looked askance at the FTC’s demarche. One can see, too, why Mr. Trump wants to redirect the FTC’s regulatory ambitions by clearing the decks of commissioners and replacing them with leaders who share his vision for promoting free enterprise unfettered by federal meddling. In this effort Mr. Trump is bolstered by the Constitution’s sole grant of all the executive branch powers to the president.

Ms. Slaughter, though, insists to the Nine that the FTC’s setup — and the president’s inability to fire agency commissioners — is meant to prioritize “the protection of individual liberty.” Such “multimember agencies,” she argues, “limit arbitrary decision-making by avoiding extreme concentrations of power.” The Constitution, though, shows no sign of the Framers anticipating anomalous agencies like the FTC.

In 1935 the Supreme Court found in Humphrey’s Executor v. United States that FTC commissioners were shielded from firing. That FDR-era precedent, though, looks shaky under the Roberts Court, which has already found that the president has broad authority to fire the heads of executive branch agencies in order to fulfill his constitutional responsibilities. Presidential power to fire agency board directors is but an extension of that logic. 

Mr. Trump’s solicitor general, John Sauer, reckons that Ms. Slaughter is a “high-level officer wielding substantial executive authority.” Mr. Trump, he adds, “has determined” that she “should not exercise any executive power, let alone significant rulemaking and enforcement powers.” If the Supreme Court agrees, the next question is whether Mr. Trump will prevail in a separate case over his firing of a member of the Federal Reserve Board, Lisa Cook.

Agencies like the FTC — as well as, more broadly, the civil service protections that Congress has bestowed on federal bureaucrats — hinder the president’s ability to execute the laws and buttress the Deep State. The Roberts Court has been vindicating this vision of presidential power, known as the unitary executive theory. Trump v. Slaughter, if it permits the president’s firing of the commissioner, could prove another step in the right direction.