Two years ago, Congress passed the landmark Affordable Care Act to provide millions of Americans with access to health care and to bring spiraling costs under control.

The ACA also is helping to protect some of our most vulnerable citizens by eliminating discriminatory practices by health insurers, ensuring that a patient’s gender is no longer a pre-existing condition and reducing the cost of prescription drugs for seniors.

These historic and long-overdue reforms also provide the necessary resources to help law enforcers recover millions of taxpayer dollars lost to fraud and abuse in the health care system.

Congress acted well within the bounds of its constitutional authority in passing the ACA. As I said when the ACA was debated in the Senate, and as I continue to believe today, the authority of Congress to pass this law falls squarely within the specific powers vested in Congress by Article I, Section 8 of the Constitution — the General Welfare Clause, the Commerce Clause and the Necessary and Proper Clause.

The provisions of the ACA are firmly rooted in what previous Congresses enacted over the past century to build and secure the social safety net. Working Americans have long been required to pay for Social Security and Medicare through payroll tax deductions. It is also not novel for Congress to pass laws affecting a health care market that makes up one-sixth of the U.S. economy, the key to satisfying the test for constitutionality under the Commerce Clause.

Yet partisan opponents of the ACA have continued their political warfare, seeking to achieve in the courts what they could not in Congress. They want judges to override legislative decisions properly assigned by the Constitution to Congress, the elected representatives of the American people. These challenges to Congress’ constitutional authority to enact the ACA have been repeatedly rejected by several federal courts. Now the Supreme Court is poised to review those decisions.

The main ACA provision attacked by partisans in the courts is the requirement that Americans have health insurance or face a tax penalty. Ironically, many of the same partisans who now claim this provision to be unconstitutional previously proposed and supported a health insurance requirement when President Bill Clinton was trying to increase access to health care.

Sen. Orrin Hatch (R-Utah), former chairman of the Judiciary Committee, proposed and supported the individual mandate during that time. This requirement was also a part of health care reform in Massachusetts supported by then-Gov. Mitt Romney and by Scott Brown, now a Republican Senator from Massachusetts. Although their views have changed, the Constitution has not.

Every Member of Congress takes an oath of office to “support and defend the Constitution of the United States.” We take this oath seriously. Arguments about the law’s constitutionality, including about the individual mandate, were considered and rejected in many Congressional committees. During the Senate debate on the ACA, I responded, publicly and on the record, to arguments about the constitutionality of this requirement. The Senate voted to formally reject a point of order claiming that the individual responsibility requirement was unconstitutional. The Senate’s judgment was that the act is constitutional.

Those who now seek to undermine the well-established constitutional authority for Congress to enact the ACA would turn back the clock to the hardships of the Great Depression, striking down principles that have been settled for nearly three-quarters of a century and standing the Constitution on its head. We must defend — and the courts should not undermine — the power given to Congress by the Constitution to protect American workers, retirees, families and consumers.

For years, we have heard Republican and Democratic Senators rightfully say that judges should not legislate from the bench. Supreme Court justices dating back to the great Chief Justice John Marshall more than 200 years ago understood the importance of not letting courts override legislative decisions properly assigned by the Constitution to the democratic representatives of the American people.

Today, the Supreme Court will hear arguments on these crucial questions. For the sake of the health and security of our nation and its citizens, the Supreme Court should not cast aside this landmark legislation and Congress’ time-honored ability to protect the American people.

Sen. Patrick Leahy (D-Vt.) is chairman of the Judiciary Committee.