As a senator, I’ve sworn an oath to the Constitution. Complying is not always convenient. Sometimes it means voting against legislation that includes policies I support. Other times, it requires standing up for our nation’s founding principles — even if it’s unpopular.

The Constitution itself is not a document of convenience. It specifies an onerous process — bicameralism and presentment — to pass legislation. It imposes a system of checks and balances among the branches. Perhaps most important, it limits the types of power the federal government can exercise.

In the words of James Madison, the father of our founding document: “The powers delegated by the proposed Constitution to the federal government, are few and defined. Those which are to remain in the state governments are numerous and indefinite.”

This basic limitation on federal powers is inconvenient for national politicians, who often seek to advance their agenda by any means. Nowhere is this more evident than with “Obamacare.”

President Barack Obama began work on a national health care plan soon after his election. Health care involves a complex set of markets already regulated by the states — and Obama found it difficult to reach his desired policy outcome using only the legitimate legislative tools available. In particular, the president found it impossible to control certain aspects of the health insurance market without an ability to control how people act within that market.

This was not the first time that federal officials had contemplated mandating how individuals participate in the marketplace. In hundreds of previous laws, such mandates could have been useful shortcuts to accomplish desired objectives. But this extraordinary exercise of coercion by the federal government was considered illegitimate and constitutionally impermissible.

Accordingly, our national leaders have never attempted to tell individuals whether and how to engage in the marketplace. Even as the size and scope of the federal government exploded after the New Deal, and Congress began to claim exceptionally broad powers, it always limited itself to regulating economic activities in which people are already engaged — rather than requiring individual economic action.

So the individual mandate of “Obamacare” represents an extraordinary departure. By seeking to compel individuals to enter into specific commercial activity in the first place, the president and the Democratic Congress disregarded any semblance of congressional restraint. They recklessly exceeded federal constitutional authority and attempted to exercise a power the Constitution reserves to the states.

As inconvenient as constitutional limits may seem, individual liberty requires that they be respected. In fact, it is precisely when temptation is greatest to disregard constitutional structures to achieve some national policy outcome that our Constitution’s limits must be enforced. As the Supreme Court once explained, though the Constitution’s restrictions may at times appear “formalistic” and may prohibit measures that are “the product of the era’s perceived necessity,” our founding document wisely “protects us from our own best intentions … so that we may resist the temptation to concentrate power in one location as an expedient solution to the crisis of the day.”

I trust that the current justices recognize this truth — and don’t allow the president illegitimate exercise of federal power to stand.

Op-ed originally published in Politico