There is a reason American soldiers, judges and political leaders must swear to protect the Constitution. America is a free, prosperous republic because of this charter we celebrate today. It is what makes us a country of laws, rather than one ruled by mobs or dictators. Straying from the Constitution will lead only to national decline.

Have we begun that decline already? Not yet. But today, we must defend the Constitution from all-out attacks by courts, legislators and regulators. Just ask Holy Cross Hospital, which will be forced by Obamacare to hire an insurer that will provide tubal ligation and abortifacients to their employees, in clear violation of their constitutionally protected freedom of religion. To keep our republic, as Benjamin Franklin enjoined us to do, we must be perpetually vigilant.

Today, we must also protect it from an unlikely source, the person who should be the main protector of our common charter and who takes a unique oath to “preserve, protect and defend the Constitution”; namely, the president of the United States. Barack Obama has sometimes shown a casual disdain for a document he clearly considers an outmoded infringement on his powers.

Mr. Obama displayed a certain ambivalence even before he became president. In one of his two autobiographies, “The Audacity of Hope,” he wrote that he couldn’t completely reject “the school of thought that sees the Founding Fathers only as hypocrites and the Constitution only as a betrayal of the grand ideals set forth by the Declaration of Independence.”

Why are progressives generally allergic to the Constitution? Mr. Obama himself laid it bare in a 2001 interview he did with Chicago public radio station WBEZ while still an Illinois state senator. In that interview, he averred, “The Constitution is a charter of negative liberties, says what the states can’t do to you, says what the federal government can’t do to you, but it doesn’t say what the federal government or the state government must do on your behalf.”

That is the crux of the problem, and as president, Mr. Obama has certainly showed zest in getting around the Constitution as he seeks to expand an activist government. Since entering the Oval Office, his constitutional violations have fallen into three main areas: executive overreach, the erection of an administrative state, and the infringement of individual rights.

Among examples of executive overreach, there is the way in which the president blithely ignored the Constitution when, acting through the Treasury Department, he unilaterally suspended in early July the employer-mandate portion of Obamacare. The statute has no provision permitting suspension by a president.

Also this summer and also on Obamacare, Mr. Obama’s administration enacted a rule by that allows members of Congress and their staffs “to use the large, tax-free subsidy that they receive for their current coverage under the Federal Employees Health Benefit Program to pay for their new exchange coverage.” All of this, again, was outside his legal authority.

Obamacare — a law that offers no end to constitutional problems — also offers examples of how the president has trampled on the Constitution in the pursuit of an ever-expanding administrative state. There were, for instance, the excessive waivers that undermined the rule of law. Mr. Obama’s Department of Health and Human Services granted more than 1,000 one-year waivers, especially to special-interest groups that are liberal allies, such as unions.

Obamacare has also been used to trample individual rights, such as the right to refuse to purchase services that violate an individual’s core religious beliefs. The Obama administration has been also contemptuous of our Second Amendment right to bear arms. It has issued no fewer than 23 executive orders curbing that basic right.

Mr. Obama and his administration are by no means alone in their attacks on the Constitution. This August, the New Mexico Supreme Court ruled that the First Amendment protection of free speech and freedom of religion did not protect Elaine Huguenin, owner of Elaine Photography, from refusing to take photographs at a same-sex union event. ‘The message a same-sex commitment ceremony communicates is not one I believe,” she said, to no avail.

If this isn’t trampling on our rights, what is?

What can we do about all this? We must be conscious of what’s happening, for starters. But we also must start thinking seriously about a constitutional-reform movement that will persuade Americans worried about current trends to register to vote. We need self-government, as the Constitution says is its purpose, “to secure the blessings of liberty to ourselves and our posterity.”

Mr. Obama and progressives in general must be put on guard that we will not allow anyone to tread on the source of our blessings.

- Jim DeMint, a former Republican senator from South Carolina, is president of the Heritage Foundation.