Ever wonder why "provide for the common defence" appears right in the preamble of the U.S. Constitution, signed 222 years ago Thursday?

Like mission statements, the preamble establishes why the Constitution was written. The framers put national defense right up with securing the "blessings of liberty" and ensuring "domestic tranquility."

A chief framer, James Madison, explained: "Security against foreign danger is one of the primitive objects of society. Without providing for our own security, we could never hope to control our own destiny or command or own fortunes."

By "primitive," Madison means basic. Providing for the common defense is a first principle of the Constitution, a fundamental obligation of the federal government. It's not optional. It's not just another budget line item or program. It's what the government is supposed to do.

National security is a precondition for everything else. None of our other rights can be enjoyed unless we are safe and secure. As my colleague at the Heritage Foundation, Matthew Spalding, argues in his new book, "Governments are instituted among men to secure rights -- which are insecure without government -- and that includes a general right to liberty free from violence (hence, the rule of law) and external threats."

We may disagree over whether the federal government should provide certain social services such as health care and how much the government should spend on them. But we should never disagree (if we take the Constitution seriously) that defending the people is a top priority. It should never be shortchanged to support activities not even envisioned in the Constitution.

Yet that is precisely what is happening. The administration is cutting vitally important defense programs. Next-generation equipment and weapons (such as planes, ships and trucks) that our armed forces will need to defend the country are on the budget chopping block. The secretary of defense claims these systems are not needed, but others argue they are being cut because President Obama has higher spending priorities, such as health care.

The line between what the federal government must do to defend us and what it should do to make us socially and economically happy has been blurred. Some politicians see national security and Social Security as constitutionally equal.

But at least one framer, James Wilson, saw it differently. In his "Lectures on Law," he argues, "Nations, as well as men, are taught by the law of nature, gracious in its precepts, to consider their happiness as the great end of their existence. But without existence, there can be no happiness: the means, therefore, must be secured, in order to secure the end."

"Happiness," in other words, is the great purpose of our lives, but safety is its essential prerequisite.

The administration is not alone in confusing the Constitution's ends and means. Even some Republican "budget hawks," eager to keep the budget under control, treat national defense as a budget line item no more important than, say, health care or education.

Yet nothing in the Constitution mandates the federal government "provide" education or health care. By refusing to make a constitutional case that defense spending should be treated differently, they unwittingly concede the claim that the federal government has a major constitutional role in these social areas.

This is a huge, practical problem. If strict constitutionalists don't stand up for a strong national defense budget, liberals certainly will not. Republicans who pose as strict constitutionalists effectively abandon the Constitution when they shortchange national defense.

This is not to say "happiness" is unimportant. After all, "promoting the general welfare" of America is one of the Constitution's objectives. But to "promote" the conditions for welfare and happiness is not the same as to "provide" them (using the Preamble's language for defense) as government programs.

Nor does it mean that the government can do anything in the name of national security. The purpose of security is to provide the precondition for enjoying the blessings of liberty, so there are inherent constitutional restrictions on how far it can go.

There are also budgetary limits. But those should be determined by the extent and nature of the threat to the country and by the country's economic capacity, rather than by budgetary competition from social programs not established by the Constitution as primary.

This logic may be hard to swallow for politicians long accustomed to using government-sponsored social programs for electoral purposes. But all it takes to see the truth of the matter is a massive national security failure, as we experienced on Sept. 11, 2001. Then the true relationship of security and happiness comes into full relief.

In the meantime, political courage is needed. A strong national defense deserves priority because, without it, all else hangs in the balance. The constitutional priority on defense exists not to deprive us of happiness, but to make it possible.

Kim Holmes is vice president of foreign- and defense-policy studies at the Heritage Foundation and author of "Liberty's Best Hope: American Leadership for the 21st Century."