A federal judge in Texas did President Trump a favor last week. It came in a decision in a case filed by the financial industry against the Labor Department to overturn an Obama-era regulation called the “fiduciary rule,” which requires financial advisers to put their clients’ interests first when giving advice and selling investments for retirement accounts. The judge, Barbara Lynn, called the plaintiffs’ objections “without merit,” “unpersuasive” and “at odds with market realities.”

If Trump were smart, he’d see the judge’s decision as a warning that he chose an ill-advised course on Feb. 3, when he sided with Wall Street, and against savers and retirees, by calling for a review and possible rollback of the rule, which is slated to take effect in April. As Judge Lynn’s decision makes clear, the rule is solid, and those behind the rollback effort, which was spearheaded by Gary Cohn, Trump’s top economic adviser and, until recently, president of Goldman Sachs, would have a difficult time asserting otherwise.

The only rationale for a rollback would be to entrench a status quo in which retirement savers forfeit an estimated $17 billion each year to stockbrokers, insurance agents and other advisers who steer them into high-cost strategies and products when comparable lower-cost options are available.

The fiduciary rule is a common-sense safeguard with far-reaching consequences. By requiring that advice be prudent and transparent about fees and conflicts of interest, it helps ensure that the billions of dollars currently siphoned off in overly expensive investments would instead remain with savers and retirees.

The financial industry has argued that the Labor Department has no authority to impose a fiduciary duty on retirement advisers. Citing federal pension law, the courts have found otherwise and have even indicated that the government waited too long to assert its authority. Judge Lynn quoted approvingly from Labor Department research that justified the need for a fiduciary rule by noting that the explosion of 401(k)s and IRAs in recent decades had shifted decisionmaking responsibility onto individuals, but without updating the regulation of advisers. That mismatch has created a confusing system, in which some advisers adhere to a fiduciary standard and many others don’t, while clients generally assume they are getting advice when they are really getting sales pitches.

Industry foes of the fiduciary rule have also argued that the rule will limit consumer choice. That is true insofar as it will remove conflicted, self-serving advice from the menu of options presented to clients. But that is not a flaw in the rule; it is the rule’s purpose. The courts have found that in crafting the rule, regulators reasonably weighed the harm to savers from biased advice against the harm to advisers from the obligation to deliver impartial advice. The result, they said, is a rule that deserves to stand.

The court’s findings will greatly complicate any review of the rule by the Trump administration, because regulators would have to rebut findings that have already withstood legal challenge.