George Miller for Congress

When the U.S. Supreme Court takes up the Affordable Care Act later this month, it will not be the first to consider its constitutionality.

Congress carefully weighed its authority in writing the law. And a majority of lower-court judges who have ruled on it, including some of the leading conservatives on the bench, have agreed that it’s constitutional. In fact, it was Reagan appointee Laurence Silberman who declared last year that challenges to the law have no support “in either the text of the Constitution or Supreme Court precedent.”

We have every reason to believe the Supreme Court will take the same view. And that’s good news because by protecting the law it will also be protecting the care of countless Americans who are already being helped by the law’s new benefits, protections and tax breaks.

One group of Americans who can look forward to the law being upheld is young adults and their parents. Historically, young Americans beginning their careers have struggled to afford health coverage, often putting off their dreams in order to take a job with health benefits.

To help these young people, the law allows many Americans under age 26 to stay on their parents’ health plans. Today, more than 2.5 million young people have already taken advantage of this benefit, giving them and their families peace of mind.

Another group of Americans who are counting on the law are the tens of millions of people now getting preventive care at no additional cost. In the past, far too many Americans went without critical cancer screenings and vaccinations because of unaffordable co-pays and deductibles, often at great risk to their health.

Now, many recommended preventive services are free for those with Medicare and private coverage. Last year, 32.5 million people with Medicare and up to 54 million Americans with private coverage got at least one free preventive service thanks to the law, a huge step forward for America’s health.

America’s small-business owners also have a lot at stake. Before the law, they paid an average of 18 percent more than their larger competitors for health coverage, sometimes forcing them to choose between providing health benefits to the employees they had and hiring new ones.

Under the law, many small-business owners are now getting tax credits to help bring those costs down. As one Montana small-business owner recently wrote: “The tax credit cut our costs by over $2,000. For a small business struggling to keep health coverage, that makes all the difference.”

The group that may have the most to gain from the health care law is America’s seniors. In addition to providing free preventive care, the law has saved 3.6 million Medicare beneficiaries with the highest prescription drug costs an average of $600 each as part of the gradual phasing out of the so-called donut hole.

And Medicare is stronger for all seniors, thanks to the law’s new protections against health care fraud. The results speak for themselves: Since 2009, health care fraud prosecutions are up 27 percent, and recoveries are up 58 percent to more than $4 billion last year.

Even those Americans who haven’t yet noticed major changes as a result of the law have a lot at stake. That’s because one of the law’s most important improvements is one that will benefit every American family: a health insurance market that’s no longer rigged in favor of big insurance companies.

Already, the law has strengthened oversight of premium hikes and established a Patient’s Bill of Rights that bans the worst abuses of the insurance industry, like canceling someone’s coverage when they get sick just because of a paperwork error.

And even bigger improvements will come in 2014 when new marketplaces will be established in every state for people and small businesses that buy their own health insurance. Plans will no longer be allowed to turn away people with pre-existing conditions. And there will be tax credits available to working families on a sliding scale to help ensure they can afford coverage.

The result will be that, for the first time in our history, all Americans will have access to affordable health coverage, even if they lose their job, change jobs, retire early or start a business.

This is a very different picture from the one conjured up by the law’s opponents before it passed. Instead of the economy crashing, more than 3 million new private-sector jobs have been created, with the health care sector leading the way. Instead of Medicare crumbling, many seniors have actually seen their premiums drop, even as they enjoy new benefits. Instead of health care providers rebelling, we’ve seen a surge of interest in the new opportunities the law gives doctors and nurses for improving care.

It’s not surprising that the law’s opponents, having lost in Congress and watched their policy case vanish, have taken to the courts to try to undo these new benefits and protections. We saw similar challenges to laws that created Social Security and established civil rights protections. Those challenges ultimately failed, and so will this one. And that’s great news for the American people.

Kathleen Sebelius, a former Democratic governor of Kansas, is secretary of Health and Human Services.