Higher-than-expected Medicare spending in 2014 and 2015 set the stage for a large premium adjustment in 2016. But, notably, the absence of inflation thanks to the drop in energy prices last year meant that seniors receiving Social Security benefits did not receive an annual cost-of-living adjustment.

The Medicare statute has a “hold harmless” provision that prevents Part B premiums from rising by more than the amount of a Social Security cost-of-living adjustment. For most beneficiaries, the provision meant that in 2016, they received no such adjustment—but also did not pay a higher Part B premium. However, nearly one-third of beneficiaries—new Medicare enrollees, “dual eligibles” enrolled in both Medicare and Medicaid (in places where state Medicaid programs pay the Medicare Part B premium), and wealthy seniors subject to Medicare means-testing—do not qualify for the provision.

The New York Times noted last fall that the hold-harmless provision, by protecting most beneficiaries, exposed some to higher increases: “If premiums are frozen for 70 percent of beneficiaries, premiums for the other 30 percent must be raised more to cover the expected increase in overall Medicare costs. In other words … the higher Medicare costs must be spread across a smaller group of people.”

Congress, seeing a dynamic in which some seniors could face a nearly 50% increase in premiums, crafted a provision to forestall such a high and sudden spike. The Bipartisan Budget Act capped Part B premium increases for 2016, paid for by a loan from the Treasury that would be repaid by seniors in future years.

The legislative language used, however, allows premium spikes to come back with a vengeance. The Bipartisan Budget Act provided that the Medicare Part B “smoothing” provision would be renewed in 2017—but only if Social Security beneficiaries received no cost-of-living adjustment at all. The trustees report out Wednesday says that beneficiaries are projected to receive a very modest adjustment: 0.2%. Although that change is relatively small, it means that the “smoothing” provisions in last year’s budget deal do not apply—and, as the Wednesday Medicare report notes, premiums for some beneficiaries “need to be raised substantially,” up to nearly $150 per month.

Before the trustees’ report was released, some experts had predicted that a series of payment reductions by the Independent Payment Advisory Board (IPAB) under Obamacare would spark talk of “death panels” in political campaigns this fall. Spending levels did not require the board to convene, making that issue moot for now. But that doesn’t mean that Medicare won’t be an issue on the campaign trail. Democrats raised the Part B premium issue last year; expect to hear much more about it before November.

This post was originally published at the Wall Street Journal Think Tank blog.