Medicare needs reform. Start with Medicare Advantage.

“SENIORS SHOULD NOT PAY TAX ON SOCIAL SECURITY!” Mr. Trump declared in a July 31 Truth Social post. This appears to mean that he would eliminate the partial income taxation of Social Security benefits, which first went into effect 40 years ago as part of a bipartisan deal to shore up the Social Security and Medicare Hospital Insurance trust funds. Proceeds from the measure help to replenish both. Mr. Trump’s suggestion would amount to a tax cut of between $1.6 trillion and $1.8 trillion over 10 years, according to the Committee for a Responsible Federal Budget. Benefits would disproportionately accrue toward relatively prosperous households, according to the Tax Policy Center.

Because of the lost revenue, Social Security’s trust fund would become insolvent one year sooner than otherwise; Medicare’s insolvency date would arrive six years ahead of current projections. And the sooner the trust funds run out of money, the sooner seniors face the prospect of mandatory benefit cuts. Mr. Trump says such a crisis might be worth precipitating: “One of the things good about that is that’s when people will make a deal,” he told Fox Business’s Maria Bartiromo. We’d feel better about that particular stratagem if he had actually backed it up with some specifics about how to make up the shortfall, but all he offered Ms. Bartiromo was “there is so much waste in our government.”

In short, Mr. Trump’s outburst about Social Security taxation will make it harder for him to keep the 2024 Republican platform’s promise to “protect Social Security and Medicare with no cuts, including no changes to the retirement age.” In fact, even before that Trump-approved document had appeared, the party had gravitated toward a position that would make it more difficult to control a key source of cost growth in the government’s health programs for seniors: Medicare Advantage.

An alternative to the “original” fee-for-service Medicare, Medicare Advantage contracts with private insurers to offer retirees a health package and manage their outpatient care, in return for an annually determined set fee. That fee is “risk-adjusted” according to the health of the insured patient population. In 2023, Medicare Advantage covered more than half of all Medicare participants for the first time in its 20-year history — 30.8 million seniors. In theory, the program taps the private-profit motive to save Medicare money and raise quality of care. In practice, insurers game the system. A recent Wall Street Journal investigation revealed that between 2018 and 2021 insurers engaged in $50 billion worth of dubious “upcoding,” tacking on extra, sometimes false, diagnoses to their enrollees’ files to inflate the risk-adjusted rates the government pays. Medicare Advantage, now a $450 billion-per-year item in the federal budget, costs more per-person than traditional Medicare.

To its credit, the Biden administration has tried to rein in Medicare Advantage, squeezing reimbursement levels and reforming risk adjustment formulas. To be clear: We’re talking about reductions in how much spending grows, not “cuts.” The administration’s most recent payment plans, announced in April, still raised Medicare Advantage by $16 billion. Nevertheless, lobbied by the insurance industry, GOP lawmakers branded these tweaks an attack on seniors. A GOP campaign ad accused Mr. Biden of “ripping health-care benefits away.” The Heritage Foundation’s Project 2025 advocated making Medicare Advantage the default option for Medicare-eligible seniors, while ending regulations that supposedly “micromanage” the program. Mr. Trump and his campaign have disavowed the Heritage policy blueprint in the face of Democratic attacks on it as a plan for extremism. But on the Medicare Advantage issue the document was hardly inconsistent with Republican thinking.

Small wonder that investors bid up stock in Medicare Advantage providers after President Joe Biden’s disastrous June 27 debate performance made a Trump victory seem more likely. The companies’ stock prices have settled back down as new developments — including Vice President Kamala Harris’s replacement of Mr. Biden at the top of the Democratic ticket and a broad market retreat — superseded the debate. The Trump-dominated GOP’s cavalier approach to entitlements looks like it’s here to stay, though. You might call it “Political Advantage.”