Editor's note: This post originally appeared in the New England Journal of Medicine's Perspective online series on April 22, 2015.

Congress has finally euthanized the sustainable growth rate formula (SGR). Enacted in 1997 and intended to hold down growth of Medicare spending on physician services, the formula initially worked more or less as intended. Then it began to call for progressively larger and more unrealistic fee cuts — nearly 30% in some years, 21% in 2015. Aware that such cuts would be devastating, Congress repeatedly postponed them, and most observers understood that such cuts would never be implemented. Still, many physicians fretted that the unthinkable might happen.

Now Congress has scrapped the SGR, replacing it with still-embryonic but promising incentives that could catalyze increased efficiency and greater cost control than the old, flawed formula could ever really have done, in a law that includes many other important provisions. How did such a radical change occur?  And why now?

The “how” was logrolling — the trading of votes by legislators in order to pass legislation of interest to each of them. Logrolling has become a dirty word, a much-reviled political practice. But the Medicare Access and CHIP (Children’s Health Insurance Program) Reauthorization Act (MACRA), negotiated by House leaders John Boehner (R-OH) and Nancy Pelosi (D-CA) and their staffs, is a reminder that old-time political horse trading has much to be said for it.

The answer to “why now?” can be found in the technicalities of budget scoring. Under the SGR, Medicare’s physician fees were tied through a complex formula to a target based on caseloads, practice costs, and the gross domestic product. When current spending on physician services exceeded the targets, the formula called for fee cuts to be applied prospectively. Fee cuts that were not implemented were carried forward and added to any future cuts the formula might generate. Because Congress repeatedly deferred cuts, a backlog developed. By 2012, this backlog combined with assumed rapid future growth in Medicare spending caused the Congressional Budget Office (CBO) to estimate the 10-year cost of repealing the SGR at a stunning $316 billion.

For many years, Congress looked the costs of repealing the SGR squarely in the eye — and blinked. The cost of a 1-year delay, as estimated by the CBO, was a tiny fraction of the cost of repeal. So Congress delayed — which is hardly surprising.

But then, something genuinely surprising did happen. The growth of overall health care spending slowed, causing the CBO to slash its estimates of the long-term cost of repealing the SGR. By 2015, the 10-year price of repeal had fallen to $136 billion. Even this number was a figment of budget accounting, since the chance that the fee cuts would ever have been imposed was minuscule. But the smaller number made possible the all-too-rare bipartisan collaboration that produced the legislation that President Barack Obama has just signed.

The core of the law is repeal of the SGR and abandonment of the 21% cut in Medicare physician fees it called for this year. In its place is a new method of paying physicians under Medicare. Some elements are specified in law; some are to be introduced later. The hard-wired elements include annual physician fee updates of 0.5% per year through 2019 and 0% from 2020 through 2025, along with a “merit-based incentive payment system” (MIPS) that will replace current incentive programs that terminate in 2018. The new program will assess performance in four categories: quality of care, resource use, meaningful use of electronic health records, and clinical practice improvement activities. Bonuses and penalties, ranging from +12% to –4% in 2020, and increasing to +27% to –9% for 2022 and later, will be triggered by performance scores in these four areas. The exact content of the MIPS will be specified in rules that the secretary of health and human services is to develop after consultation with physicians and other health care providers.

Higher fees will be available to professionals who work in “alternative payment organizations” that typically will move away from fee-for-service payment, cover multiple services, show that they can limit the growth of spending, and use performance-based methods of compensation. These and other provisions will ramp up pressure on physicians and other providers to move from traditional individual or small-group fee-for-service practices into risk-based multi-specialty settings that are subject to management and oversight more intense than that to which most practitioners are yet accustomed.

Both parties wanted to bury the SGR. But MACRA contains other provisions, unrelated to the SGR, that appeal to discrete segments of each party. Democrats had been seeking a 4-year extension of CHIP, which serves 8 million children and pregnant women. They were running into stiff head winds from conservatives who wanted to scale back the program. MACRA extends CHIP with no cuts but does so for only 2 years.  It also includes a number of other provisions sought by Democrats: a 2-year extension of the Maternal, Infant, and Early Childhood Home Visiting program, plus permanent extensions of the Qualified Individual program, which pays Part B Medicare premiums for people with incomes just over the federal poverty thresholds, and transitional medical assistance, which preserves Medicaid eligibility for up to 1 year after a beneficiary gets a job.

The law also facilitates access to health benefits. MACRA extends for two years states’ authority to enroll applicants for health benefits on the basis of data on income, household size, and other factors gathered when people enroll in other programs such as the Supplemental Nutrition Assistance Program, the National School Lunch Program, Temporary Assistance to Needy Families (“welfare”), or Head Start. It also provides $7.2 billion over the next two years to support community health centers, extending funding established in the Affordable Care Act.

Elements of each party, concerned about budget deficits, wanted provisions to pay for the increased spending. They got some of what they wanted, but not enough to prevent some conservative Republicans in both the Senate and the House from opposing final passage. Many conservatives have long sought to increase the proportion of Medicare Part B costs that are covered by premiums. Most Medicare beneficiaries pay Part B premiums covering 25% of the program’s actuarial value. Relatively high-income beneficiaries pay premiums that cover 35, 50, 65, or 80% of that value, depending on their income. Starting in 2018, MACRA will raise the 50% and 65% premiums to 65% and 80%, respectively, affecting about 2% of Medicare beneficiaries. No single person with an income (in 2015 dollars) below $133,501 or couple with income below $267,001 would be affected initially. MACRA freezes these thresholds through 2019, after which they are indexed for inflation. Under previous law, the thresholds were to have been greatly increased in 2019, reducing the number of high-income Medicare beneficiaries to whom these higher premiums would have applied. (For reference, half of all Medicare beneficiaries currently have incomes below $26,000 a year.)

A second provision bars Medigap plans from covering the Part B deductible, which is now $147. By exposing more people to deductibles, this provision will cause some reduction in Part B spending. Everyone who buys such plans will see reduced premiums; some will face increased out-of-pocket costs. The financial effects either way will be small.

Inflexible adherence to principle contributes to the political gridlock that has plunged rates of public approval of Congress to subfreezing lows. MACRA is a reminder of the virtues of compromise and quiet negotiation. A small group of congressional leaders and their staffs crafted a law that gives something to most members of both parties. Today’s appalling norm of poisonously polarized politics make this instance of political horse trading seem nothing short of miraculous.