This opinion piece was first published in The Wall Street Journal.

Democrats have made clear that if they win the presidency and Congress in November, they will attempt to take over the Supreme Court as well. Shortly after ending his re-election campaign, President Biden put forth a package of high-court “reforms,” including term limits and a “binding” ethics code designed to infringe on judicial authority. Kamala Harris quickly signed on, and Majority Leader Chuck Schumer has made clear that bringing the justices to heel is a top priority.

Democrats proclaim their devotion to democratic institutions, but their plan for the court is an assault on America’s basic constitutional structure. The Framers envisioned a judiciary operating with independence from influences by the political branches. Democratic “reform” proposals are designed to change the composition of the court or, failing that, to influence the justices by turning up the political heat, as President Franklin D. Roosevelt achieved with his failed 1937 court-packing plan.

Now as then, the court stands between a Democratic administration and its ambitions. The reformers’ beef is precisely that the court is doing its job by enforcing constitutional and statutory constraints on the powers of Congress and the executive branch.

Roosevelt sought to shrug off limits on the federal government’s reach. What’s hamstrung the Obama and Biden administrations is the separation of powers among the branches. President Obama saw his signature climate initiative, the Clean Power Plan, stayed by the court, which later ruled that it usurped Congress’s lawmaking power. The Biden administration repeatedly skirted Congress to enact major policies by executive fiat, only for the courts to enjoin and strike them down. That includes the employer vaccine mandate, the eviction moratorium and the student-loan forgiveness plan.

That increasingly muscular exercises of executive power have accompanied the left’s ascendance in the Democratic Party coalition is no coincidence. The legislative process entails compromise and moderation, which typically cuts against radical goals. That was the lesson self-styled progressives took from ObamaCare, which they’ve never stopped faulting for failing to establish a government medical-insurance provider to compete directly with private ones. Similarly, Congress has always tailored student-loan relief to reward public service and account for genuine need.

Then there’s the progressive drive for hands-on administration of the national economy by “expert” agencies empowered to make, enforce and adjudicate the laws. The Supreme Court has stood as a bulwark against the combination of powers that James Madison pronounced “the very definition of tyranny.” Decisions from the 2023-24 term cut back on agencies’ power to make law through aggressive reinterpretation of their statutory authority, to serve as judge in their own cases, and to evade judicial review of regulations alleged to conflict with statute. By enforcing constitutional limits on the concentration of power in agencies, the Roberts court has fortified both democratic accountability and individual liberty.

That explains the Democratic Party’s attacks on the court. The New York Times’s Jamelle Bouie recently praised Mr. Biden for identifying the court as the “major obstacle to the party’s ability” to carry out its agenda and commended the president’s “willingness to challenge the Supreme Court as a political entity.” That explains the ginned-up “ethics” controversies: The aim is to discredit the court, as has become the norm in political warfare.

An even bigger lie is the refrain that the court is “out of control” and “undemocratic.” Consider the most controversial decisions of recent terms. Dobbs v. Jackson Women’s Health Organization (2022) returned the regulation of abortion to the democratic process. West Virginia v. EPA (2022) and Loper Bright Enterprises v. Raimondo (2024) constrained agencies’ power to say what the law is, without denying Congress’s power to pursue any end. Securities and Exchange Commission v. Jarkesy (2024) elevated the Seventh Amendment right to a jury in fraud cases over the SEC’s preference to bring such cases in its own in-house tribunals. And Trump v. U.S. (2024), the presidential immunity ruling, extended the doctrine of Nixon v. Fitzgerald (1982) to cover criminal charges as well as lawsuits, without altering the scope of presidential power one iota.

Meanwhile, the administrative state has scored wins in some of this year’s cases. In Consumer Financial Protection Bureau v. Community Financial Services Association, the justices rejected a challenge to the CFPB’s open-ended funding mechanism. A ruling to the contrary could have spelled the agency’s end. In Moody v. NetChoice, it reversed a far-reaching injunction restricting agencies’ communications with social-media companies seeking to censor content. And in Food and Drug Administration v. Alliance for Hippocratic Medicine, it reversed another injunction, against the FDA over its approval of an abortion pill. The last two decisions were notable as exercises of judicial restraint. In both cases, the court found the challengers lacked standing to sue.

What Mr. Biden, Ms. Harris, Mr. Schumer and their party are attempting to do is wrong and dangerous. They aim to destroy a branch of federal government. For faithfully carrying out its role, the court faces an unprecedented attack on its independence, beyond even Roosevelt’s threats. Unlike then, however, almost every Democratic lawmaker and official marches in lockstep, and the media, which were skeptical of Roosevelt’s plan, march with them.

As Alexander Hamilton observed, the “independence of the judges” is “requisite to guard the Constitution and the rights of individuals” from the actions of “designing men” set on “dangerous innovations in the government.” The political branches have forgone their own obligation to follow the Constitution, which makes the check of review by an independent judiciary all the more essential. Ms. Harris and Mr. Schumer would put it under threat.

Mr. Rivkin served at the Justice Department and the White House Counsel’s Office in the Reagan and George H.W. Bush administrations. Mr. Grossman is a senior legal fellow at the Buckeye Institute. Both practice appellate and constitutional law in Washington.