Fifty years ago this week, Lyndon Johnson signed into law Medicare, the first truly ambitious realization of the long-harbored liberal goal of securing a role for the federal government in providing health care to the poor and the elderly. He declared:

“No longer will older Americans be denied the healing miracle of modern medicine. No longer will illness crush and destroy the savings that they have so carefully put away over a lifetime so that they might enjoy dignity in their later years.”

What should we remember about Medicare’s passage and history, a half century later?

Jonathan Cohn has a good piece running through all of the ways in which Medicare has improved the lives of countless Americans; about the ways in which it’s fallen short; about early conservative attacks on the program as socialism and worse; and about the continued conservative campaign to undermine its core coverage guarantee, which will likely be a key point of argument in 2016 and beyond.

I wanted to focus on another lesson that can be drawn from Medicare’s history. It’s a reminder of how long it takes to secure true progressive reform, and how hard it is to continue to build on such change. This should be kept in mind by those who are, understandably, frustrated by the opposition that continues to bedevil Obamacare’s coverage expansion, and by the many other ways in which progressive change has been stymied during the Obama years.

Medicare is taken for granted as a pillar of American life today. But it was only achieved more than 15 years after the push for government health care got underway, when President Harry Truman called for national health insurance in 1949. Medicare became law a full eight years after Congressional Democrats decided, in 1957, to try to secure a much narrower plan — one only for the elderly — than Truman wanted. In a sense, Medicare itself represented a scale-back of liberal ambitions.

Medicare was difficult to achieve, even though the American public was less ideologically divided over the proposal than it has been over, say, the Affordable Care Act. According to Julian Zelizer’s wonderful book on the Congressional battles over the Great Society, polling in the mid-1960s showed that a majority of Americans favored government-funded health care for the elderly over a privately-financed program.

Yet while Medicare was widely hailed as a groundbreaking moment for American health care policy, it actually disappointed liberals in some respects. As Zelizer writes, the legislation “was a far cry from the program President Truman had proposed,” and “provided federal support only to a segment of the population.”

Indeed, liberals were destined for further disappointment. Medicare was seen by many of them at the time as a first step towards universal national health care. But politics and history intervened. Thanks in part to the northern white backlash against other achievements of the era — particularly in the area of civil rights — conservatism enjoyed a revival that stalled and even chipped away at the Great Society’s gains and laid the groundwork for the Ronald Reagan ascendance.

Medicare endured, obviously, as neither Richard Nixon nor the conservatives of the Reagan era succeeded in substantially undoing the Great Society. But an astonishing 45 years — nearly a half century — had to pass between the creation of Medicare and the signing of Obamacare. This is surely not what liberals expected as they watched LBJ sign the first major expansion of government health care in the mid-1960s.

Not only that, but in some respects, Obamacare itself fell short of the long-term promise those liberals had hoped would be brought within reach by the achievement of Medicare. The Affordable Care Act, of course, is a far cry from the single payer system many liberals still hope for, and its only public component — the public option — died in Congress.

“Obamacare is less radical than Medicare was,” Larry Levitt of the Kaiser Family Foundation tells me. “Medicare was created as a government insurance plan. And Obamacare rests on a foundation of private insurance.”

Yet Obamacare has virtually no support among GOP lawmakers. While we can endlessly debate whether this was Obama’s fault, the fact remains that Johnson and Congressional Democrats were able to secure substantial GOP support for Medicare — enabling them to give that expansion of government health care a bipartisan stamp of approval. The Affordable Care Act does not have that.

And GOP opposition to the ACA continues to represent a serious obstacle to our progression towards universal health care. We don’t know how long that will last. Medicare has broad, deep public support, and Obamacare doesn’t. We also don’t know how long that will last.

Progressive change is hard. It proceeds in fits and starts, with long periods of stagnation intervening and major setbacks stalling or even reversing gains. Be patient, folks.