Attorney General William Barr has faced harsh criticism for his problematic treatment of the Mueller report, which some have suggested appeared to be calculated to benefit the president. But a different action Barr recently took at President Donald Trump’s behest should be equally concerning. Last month, the attorney general announced that the United States will cease defending any portion of the Affordable Care Act in the courts. Instead, the DOJ will join a number of state attorneys general in challenging the constitutionality of the entire ACA, following the effective repeal of the individual mandate by Congress.

This comes after the DOJ stopped defending the constitutionality of the ACA’s protection of insurance coverage for those with preexisting conditions last year. In taking the position that the entire ACA is constitutionally void, Barr abandoned a long-standing principle that the Department of Justice is duty-bound to defend the constitutionality of federal laws. In the words of one of Barr’s predecessors, such an action by the nation’s chief law enforcement officer may jeopardize the equilibrium of our constitutional system.

Barr has all but acknowledged that the arguments against the ACA’s constitutionality, although they were accepted by one trial judge, are far from compelling; in fact, most observers (including some opponents of the law) consider them to be extremely weak. But during testimony before Congress this week, Barr stated that he nonetheless feels duty-bound to attack the ACA in the courts because Trump, after failing to convince a majority of the Senate to vote in favor of repealing the ACA, is now eager to see the act nullified by the courts instead.

Barr’s decision is at direct odds with a policy upheld for decades by attorneys general in Republican and Democratic administrations. As President Ronald Reagan’s first attorney general, William French Smith, wrote in 1981, the DOJ has “a duty to defend the constitutionality of an Act of Congress whenever a reasonable argument can be made in its support.”

While serving as President Jimmy Carter’s attorney general, Benjamin Civiletti explained that this policy is rooted in the Constitution’s separation of powers. While the courts are charged with protecting “both the government and the citizenry from unconstitutional action, legislative and Executive [ … ] only the Executive Branch can execute the statutes of the United States,” including by defending them in the courts. Therefore, “if executive officers were to adopt a policy of ignoring or attacking acts of Congress whenever they believed them to be in conflict with the provisions of the constitution, their conduct in office could jeopardize the equilibrium established within our constitutional system.”

Prior attorneys general recognized only one extremely narrow exception to this obligation to defend the nation’s laws: when an attorney general concludes that there is no reasonable argument in favor of a federal statute’s constitutionality. As Civiletti put it, where “everything in our constitutional jurisprudence inescapably establishes” that a law is unconstitutional, then the Executive Branch can properly decline to defend or enforce it.

Until recently, conservative legal scholars emphasized the narrowness of this exception. Many of them assailed Eric Holder, President Barack Obama’s attorney general, for choosing to end the DOJ’s defense of a portion of the Defense of Marriage Act denying federal government recognition to same-sex marriages. While Holder argued that changes in Supreme Court jurisprudence left no reasonable basis to defend the law, his opponents contended that Holder was being disingenuous and placing ideological concerns above his duty to defend a duly enacted federal law. In fact, conservative legal advocate Edward Whelan continued to assail Holder’s decision to abandon the defense of DOMA even after the law was struck down by the Supreme Court, calling it a “shameful moment in politicized government lawyering and … a dangerous precedent that deserves condemnation.”

Barr’s decision to attack the ACA in court, however, sets a far more dangerous precedent. Unlike Holder, Barr does not even make a pretense of arguing that there is no reasonable argument in favor of the ACA’s constitutionality. Rather, during his recent testimony, Barr explained to Republican Sen. Susan Collins that he acceded to the president’s demand to attack the ACA in the courts because the arguments mounted against the law are “defensible and reasonable.” Barr’s reasoning turns long-standing DOJ policy on its head, allowing the attorney general to abandon a federal law so long as there is some plausible basis to question its constitutionality—even if there are reasonable, or even compelling, arguments to be made in support of the law’s validity.

When pressed, Barr asserted that supporters of the ACA have “nothing to worry about” if they are right that the arguments the DOJ is adopting against the ACA’s constitutionality are weak. “I think people should take a deep breath,” Barr said. “If this is such a wacky position that the administration is taking, then there’s nothing to fear. Then the law will be upheld.” Just “[l]et the courts do their job,” the attorney general suggested. But Barr’s argument misses the point. As his predecessor Civiletti observed decades ago, while it is the courts’ constitutional “job” to protect against “unconstitutional action,” the Constitution assigns the executive branch the obligation to faithfully defend the nation’s laws, including before the courts. It is, therefore, in Ed Whelan’s words, shameful for the DOJ to abandon that job.

Barr’s decision to attack the ACA in court sets a far more dangerous precedent.

Barr’s DOJ is already taking full advantage of its newfound freedom to pick and choose which federal laws to defend in court. Just this week the solicitor general informed House Judiciary Committee Chairman Jerrold Nadler that the DOJ has chosen to cease defending the constitutionality of a federal law criminalizing the practice of female genital mutilation and cutting (FGM/C).

Earlier this month, the acting director of the DOJ’s Office on Violence Against Women decried the “horrific crime of” FGM/C,” explaining that “at least 513,000 women and girls in the United States have suffered or are at risk of becoming victims” of it. The FBI, ICE, and the State Department have all recently likewise reiterated a commitment to using the full force of the federal government against this heinous practice.

But the federal law against FGM/C is largely grounded in Congress’ regulatory authority under the Commerce Clause, which conservative legal scholars and judges have long been intent upon limiting on principles of federalism; the other rationale for the statute—that it implements Congress’ power to enforce an international human rights treaty—is similarly objectionable to strong advocates of federalism. Accordingly, as in the case of the ACA, the DOJ is abandoning its defense of a law against this heinous practice for transparently ideological reasons.

In explaining his decision to mount a litigation effort against the ACA, Barr stated that he serves the president and other “stakeholders” in the executive branch. Therefore, if the president directs him to attack a statute, even one Barr seems to believe will ultimately be upheld in the courts, the attorney general considers himself duty-bound to oblige. This goes to the heart of Barr’s misconception of his role as attorney general. He is the lawyer for the United States, not for Donald Trump. As such, he and the DOJ owe a duty to uphold and defend the laws of the nation, even if the president does not like them, just as he is obligated to disclose facts uncovered by Robert Mueller, even if they are harmful to Donald Trump. Barr’s failure to abide by such foundational principles truly threatens the equilibrium of our constitutional system.