You never get a second chance to make a first impression. But at the end of this month, the new health care law will get a third chance to make a decent impression — finally.

Everyone who believes that reducing economic insecurity requires a strong government role in guaranteeing health insurance to all Americans should take advantage of this opportunity. This obligation falls on President Barack Obama, but it also encompasses Democratic members of Congress who voted for the law but now fret over the political consequences of a full-hearted embrace of the system they created. They can’t just duck.

The first two opportunities to make the case were blown. During the battle to pass the law, its opponents did a far better job of tarring it than its sponsors did of extolling it. Last fall, the crash of the HealthCare.gov website made a hash of its debut.

But the end of the enrollment period on March 31 provides an opening to count up the number of Americans who now have insurance because Congress acted. The pace of sign-ups has risen sharply in recent weeks. Many Americans want what the Affordable Care Act (ACA) is offering. And yes, its allies should stop using that politically charged “Obamacare” label. This is about health insurance, not the man in the White House.

The ACA is worthy of defense on its merits because it begins solving problems that Americans have always wanted solved. These include outlawing discrimination against those with pre-existing conditions and doing away with the fears of those could never afford coverage or temporarily lost it during hard times.

But a larger principle is at stake, too. In an article last week about Americans for Prosperity, the group backed by Charles and David Koch, New York Times writers Carl Hulse and Ashley Parker made the essential point. The Koch effort, Hulse and Parker wrote, is “not confined to hammering away” at the ACA. “They are also trying to present the law as a case study in government ineptitude to change the way voters think about the role of government for years to come.”

The underlying fight is thus over social insurance approaches that have been part of the fabric of American life since the progressive era and the New Deal. If opponents of the ACA can discredit it, they can move on to demonize other necessary public programs — and undercut arguments for further government efforts to ease inequalities and injustices.

This agenda is rooted in the idea that the United States was better off in pre-progressive days when it relied on private and community charity to deal with social problems and economic upheavals. One of the best summaries of this thinking was a speech last fall by Sen. Mike Lee, R-Utah, at the Heritage Foundation.

Highlighting the work of “voluntary civil society,” Lee claimed that progressives who favor government programs “do not trust individuals to join together voluntarily and organically to improve each other’s lives and meet common challenges.”

But history is not on the side of this view, argues Mike Konczal, a fellow with the Roosevelt Institute. Even on its own terms, the argument ignores how government programs in fact strengthen civil society. They enable private charity “to respond with targeted and nimble aid for individuals and communities, rather than shouldering the huge, cumbersome burden of alleviating the income insecurities of a modern age.”

In a new article in the journal Democracy (I chair its editorial committee), Konczal notes that our social insurance and welfare programs arose precisely because private charity utterly failed during the Great Depression. It’s no criticism of their good work to note that charities run into trouble when help is most needed. This happened again during the Great Recession. Charitable giving, Konczal notes, fell 7 percent in 2008 and another 6.2 percent in 2009, even as state and local governments were also cutting back.

And most charitable giving simply isn’t directed to our society’s less fortunate. Konczal cites the finding of Indiana University’s Center for Philanthropy that “only one-third of charitable giving actually goes to the poor.” National initiatives for economic security fill the gaps and keep the economy going when incomes lag.

A just society, Konczal concludes, demands an energetic government response to “the Four Horsemen of accident, illness, old age and joblessness.”

Say what you will about the Koch brothers: They fully understand the long-term importance of the health care battle. Supporters of indispensable government programs must be as shrewd and as committed as they are.