When Texans, including Governor Greg Abbott, give credence to the possibility that the U.S. military's Jade Helm 15 training exercise is a pretext to occupy Texas and confiscate the people's guns, it's easy to dismiss them as paranoid fantasists. And certainly, those concerns are demonstrably paranoid. But it's paranoia that reflects a quintessentially American concern about the risks of a standing army -- one that goes back to James Madison, and is tied to the origins of the Second Amendment.

For Madison, the worry about a standing army wasn't minor. A standing army was understood to pose an existential threat to a self-governing republic. The paradigm case was Rome, which had devolved from a republic into an unfree empire ruled by Caesars precisely because generals used the army to coerce the city into obedience. Madison cited Rome at the constitutional convention in the course of asserting that "the means of defense against foreign danger, have been always the instruments of tyranny at home."

And Madison believed that modern absolutist rule similarly depended on the maintenance of standing armies by rulers. "Throughout all Europe," he argued, "the armies kept up under the pretext of defending, have enslaved the people." But even the Constitution as drafted -- which gave Congress, not the president, the power to declare war and raise an army -- didn't satisfy skeptics that the Republic would be sufficiently protected. At the state ratifying conventions, there were calls for a constitutional amendment to protect against the danger of the standing army.

CartoonDavies' latest cartoon: HUD or huh?CommentSubmit your letterReader essaysGet published in Newsday

Those calls led to what became the Second Amendment: that "a well regulated Militia, being necessary to the security of a free State, the right of the People to keep and bear Arms, shall not be infringed." The idea was that militias -- self-regulating organizations of civilians who trained to go to war as needed -- were necessary to protect freedom against tyranny.

In other words, because a standing army would inevitably subvert a free state, such a state required instead militias to defend itself. A government that banned militias would be trying to consolidate power under a standing army. The Second Amendment was intended to keep the militia structure primary and permanent.

Madison clung to the worry about standing armies all the way into the War of 1812, when he was president. His war strategy was to invade Canada quickly, before Britain could send troops to defend it, and force Britain to capitulate on trade restrictions that it had failed to remove despite years of U.S. economic sanctions. Because the U.S. had almost no standing army, the attack strategy relied mostly on militia. Those militia failed abjectly as an offensive force. Some refused to cross the border into Canada, claiming that under the Constitution and the laws of their states, militia could only be used in defense, not as an invading force abroad. Others just turned and ran.

advertisement | advertise on newsday

The result was a war that dragged on indecisively until, after the defeat of Napoleon's army in Russia, the British were able to turn the tables and send invading forces to North America. The militia did a bit better in defending against British attacks at Baltimore, Plattsburgh and eventually New Orleans. But elsewhere they performed abominably, most famously at the brief, ignominious Battle of Bladensburg, where they turned tail and let an invading British force march into Washington unopposed. Madison had to flee the battle and the city -- and the British torched the Capitol and the White House.

Madison learned the lesson of Bladensburg. When the war was over, and his popularity was at its peak, he called for a small but permanent standing army to provide for national defense -- a view that he would have considered heresy before experience taught him the limits of militia.

Subsequently, the U.S. did in fact grow into a continental and then global empire, expansion that couldn't have happened had the nation relied only on militia and eschewed a standing army. And it's maintained its character as a republic of a kind.

Sign up for The Point

Go inside New York politics.

But the power of the modern presidency vastly outstrips what Madison would have believed appropriate. A president can make certain kinds of war without Congress, as Barack Obama did for a time in Libya.

The Texans who fret about the U.S. Army occupying Texas are thus doing Americans the service of reminding the nation of its anti-militaristic, anti-imperial origins. Their worry about their guns is an imperfect echo of the Second Amendment's original purpose. The gun-toting folks' role as the nation's unconscious conscience isn't an accident. In a general sense, they often share the framers' classical republican-libertarian values of self-government and the avoidance of foreign entanglements. When the country today updates those values to the point of rejecting them, it's important to know that we're doing so -- and to recognize the costs.

And after all, the Jade Helm exercise is in fact to train the army in the techniques of occupation, a military training necessity born of U.S. occupying missions in Afghanistan and Iraq. It's worth remembering that the British Empire also occupied both -- with not much more success than the U.S has had. Madison believed that empires occupy, republics defend. By that measure, the U.S. is no longer the republic the framers made.

Noah Feldman, a Bloomberg View columnist, is a professor of constitutional and international law at Harvard and the author of six books, most recently "Cool War: The Future of Global Competition."