Even America's bitterest enemies understand why we mark July Fourth with parades, speeches and fireworks: to celebrate the signing of the Declaration of Independence. We're proud of our nation, and justifiably so.

So why do we virtually ignore Sept. 17? That's the date in 1787 when our Founding Fathers signed the Constitution. And if any one factor can explain why our republic has endured - indeed, thrived - for 223 years, it is this unique charter, which outlines the form of government best designed to safeguard "life, liberty, and the pursuit of happiness," as the Declaration puts it.

Yet today, on many issues, this vital document is frequently ignored, even undermined, by some of the very people who have taken a public oath to uphold it.

Consider the debate over Arizona's immigration law. Here we have a state understandably frustrated by the federal government's failure to control the flow of illegal immigrants. So it passed a law to enforce immigration laws already on the books. Hysteria ensues. The Justice Department demands that the law be struck down.

Susan R. Bolton, the federal judge who subsequently ruled on the law, didn't go that far, fortunately. But she did suspend certain parts of it, such as a provision authorizing the arrest of an individual "where reasonable suspicion exists that the person is an alien and is unlawfully present in the United States."

Why? Because that might go against the Obama administration's practice of not enforcing immigration law in many of these cases. But what she could not say is that the Arizona law was somehow inconsistent with the actual federal immigration law. She simply relied on judicial fiat to produce a conclusion that flouts precedent and tradition. Is she unaware that it's her job to interpret the law, not rewrite it?

We see this same destructive impulse in the fight over California's referendum on same-sex marriage. The state followed the law to the letter, allowing its citizens to make their voices heard on this important issue. Then along comes U.S. District Judge Vaughn Walker, who strikes down Proposition 8.

Did he refute the substantial evidence in favor of Proposition 8? No, he didn't even mention it. Did he cite binding Supreme Court precedent to justify his action? No, he ignored it. In 1972's Baker v. Nelson, Minnesota was accused of violating the Constitution by issuing marriage licenses only to opposite-sex couples. The Supreme Court unanimously threw out the case, finding that no substantial federal question existed. In short, it was a state matter.

Now, no matter what Judge Walker thinks about Baker, he has no business disregarding it. As former U.S. Attorney General Edwin Meese III explained in an Op-Ed for The Washington Post, "Walker's ruling is indefensible as a matter of law." The judge also should have weighed the evidence supplied by Proposition 8's supporters. Instead, we have a judge acting outside the boundaries laid down by the Constitution.

Judges aren't the only offenders. In the matter of health care reform, lawmakers in Congress are the ones acting as if their power is limitless. Supporters of Obamacare claim they can regulate (i.e., force you into buying) health insurance because the Constitution allows Congress to regulate commerce. Just to be clear: The argument is that your decision not to buy something is commerce. The Supreme Court has ruled repeatedly that the commerce clause has limits, and that Congress saying that it's regulating commerce doesn't necessarily make it so. Yet some in Congress act as if they can compel a free people to do anything they want.

Enough. It's easy to see why Constitution Day is so important: We need judges who interpret this vital document as it was written, not as they wish it were written. That's the only way to ensure it will be around for another two centuries.

Ed Feulner is president of the Heritage Foundation.