The Affordable Care Act (ACA), a signature achievement of President Obama, represents one of the biggest overhauls of the modern health system. Implementing it was, and still is, one of the greatest challenges facing policymakers and health-care leaders alike.

Regardless of its fate as Congress tries to repeal and replace the law, and regardless of a person's feelings about what many call "Obamacare," there are lessons to be learned from the execution of such a large-scale and wide-ranging change to government and industry.

To get a sense of those lessons, two health policy experts surveyed a variety of state leaders -- including governors, legislators and Medicaid directors. Their findings were published last month by the Milbank Memorial Fund.

For states, the creation of online marketplaces and the expansion of Medicaid -- if they chose to do so -- required the biggest undertaking. Policy analysts had to be hired; IT contracts had to be procured; and educational campaigns had to be launched.

"Even states with large bureaucracies and a tradition of policy innovation could not be expected to possess all the needed professional expertise, the human and financial resources and the institutional infrastructure required for this extraordinary situation," the report notes.

Exchanges are up and running, and every state has had a decrease in the number of uninsured because of the law. But getting to that point was more difficult for some states than others.

Oregon, for example, had such substantial technical difficulties with its exchange that it was mired in lawsuits with the contractors who built it and eventually abolished it.

Perhaps unsurprisingly, the three critical factors that officials said swayed the degree of success they had were money, expertise and political support (or lack thereof).

“It was clear in some states, without that input from the executive office, nothing would have happened,” says Pierre-Gerlier Forest, co-author of the report and director of the school of public policy at the University of Calgary.

This is most evident in states' decisions on whether to expand Medicaid to more low-income people. Without the support of a governor, Medicaid expansion was dead on arrival. In many states, governors were on board with the idea but couldn't convince their lawmakers. In some of these states, legislators eventually warmed up to Medicaid expansion and agreed to implement it, just later than their peers.

Seven years after the law was first signed, these debates are still happening. Several states have re-examined the prospect of expanding Medicaid since congressional Republicans' first replacement bill failed to garner enough support to be voted on.

In Kansas, for example, Gov. Sam Brownback recently vetoed a Medicaid expansion bill. The legislature has signaled that it will revisit the issue, but David Helms, co-author of the study and professor of health policy at Johns Hopkins University, says that “without the governor's support, it’s hard to move."

In some states, disagreements between the governor and lawmakers pushed policy changes forward. Just look at Arkansas.

The state's leaders cooperated and compromised to "make parts of this law work for all of us," says John Selig, the former head of the state's Department of Human Services. Together, they pioneered the so-called private option, which became a model for several other states with split leadership.

Leaders in Kentucky, another state with split leadership at the time, came together to create what many say was the national example for a well-run marketplace. It was dismantled, though, by newly-elected Gov. Matt Bevin in 2016.

Health care is complex, and many of its experts work outside of government. One of the other huge obstacles to a smooth implementation, officials commonly said, was not being able to afford the best and brightest minds in the field.

“How do you acquire qualified enough staff when you have procurement standards that don’t afford the ability to hire the people you want?” says Forest.

In some instances, officials complained that it wasn't necessarily the quality of their staff but the quantity.

“It’s clear to me that a legislature that tries to reduce the size of government generally removes policy and analytical positions, and that removes the capacity to get things done,” says Chuck Hunter, former minority leader of the Montana state House.

When states did struggle to afford the necessary brainpower, a somewhat hidden player often stepped in: foundations. The Robert Wood Johnson Foundation, The Commonwealth Fund and the Kaiser Family Foundation are a few examples of organizations that filled either financial or analytical gaps.

“There is no equivalent elsewhere in the world," says Forest. "It’s a real strength of the U.S. system that it has these national foundations as levers."

The Milbank Memorial Fund created the Reforming States Group, a bipartisan group of state leaders who met regularly to discuss challenges in implementing the ACA. State leaders say those opportunities to meet and talk freely were invaluable.

“That kind of networking in a nonpartisan way exposed me to what was and wasn’t working in other states," says Hunter. "I can say it was critically important to what we ended up doing in Montana."

Helms, the report's co-author, says the law has forced some state lawmakers to put their own political careers on the line. It’s something he says policymakers haven't been given enough credit for.

“We haven’t fully appreciated what it was like for these state leaders under such political pressure, especially in states with split control in their state legislatures. They were always under the political gun. Now we have 24 million more people covered."

*CORRECTION: A previous version of this mistakenly reported that the report was published in The Milbank Quarterly.