Paul McHale

is a former member of Congress (1993-99) and assistant secretary of defense (2003-09) and a retired Marine colonel with 33 years of active and reserve service

There is a military term of art that has deep significance in our fight against ISIS. It captures the idea that there is an identifiable source of enemy power that, if successfully attacked, will lead to our enemy's strategic defeat. That enemy strength (and potential vulnerability) is called its "center of gravity."

In my judgment, ISIS can be contained and then destroyed, but that goal will not be achieved by brute military power. ISIS's center of gravity exists far beyond the battlefield. It exists in the hearts, minds, and aspirations of the young men and women who are drawn to the cause of violent Islamic extremism. Killing ISIS fighters at the front end of the combatant pipeline has value - but closing the pipeline of ISIS recruiting is the real center of gravity.

Throughout U.S. history, our men and women in uniform have fought and died for a noble cause: the unwavering defense of individual freedom. They understood - often when our politicians did not - that there was something at stake that transcended self-interest. Yes, to be effective, military forces need to be well-trained and equipped. And they need to be well-led. But most important, they need to believe that they are fighting for something worthy of their blood and sacrifice.

Stripped of its pretense, ISIS is fighting for a malignant ideology. It commits acts of barbarism in the name of God. It brutally subjugates women. It abhors modern concepts of education and culture. It decapitates prisoners for failure to recite a particular religious creed. In the pursuit of its relentless goal to crush individual liberty, ISIS is simply the current manifestation of violent intolerance - the ancient and darkest side of human nature. For ISIS and its leaders, diversity is not a positive social value, it is a sin punishable by death.

What needs to be defeated is not so much the army of ISIS, but the idea of ISIS.

Our fight against ISIS - and other terrorist groups that espouse a similar ideology - is not an attack upon a particular religion or a clash of civilizations. It is an affirmation of civilization itself - a vigorous defense of religious tolerance, sanctity of conscience, and individual liberty. And it reflects the belief that governmental power, to be legitimate, must be guided by these principles.

When I worked at the Pentagon, I often heard references to the "Battle of Ideas." That term was meant to describe the inevitable conflict between our core beliefs and those espoused by Islamic extremists. In truth, that battle has never been fought - and it is long overdue. If fought wisely by us, it will cripple the recruiting appeal of ISIS.

I believe President Obama should look to the historic example of Franklin Roosevelt. He should read FDR's Jan. 6, 1941 speech, "The Four Freedoms." It is an enduring commitment to freedom of speech and expression, freedom of worship, freedom from want, and freedom from fear - everywhere in the world. And then, using every available tool of social media, and hopefully with reinforcing diplomatic support, the president should follow Roosevelt's advice: "As men do not live by bread alone, they do not fight by armaments alone. Those who man our defenses, and those behind them who build our defenses, must have the stamina and courage which come from an unshakable belief in the manner of life which they are defending."

That message (from Roosevelt and hopefully Obama) differentiates us from our ISIS enemies, and it is the key to our strategic success. But to achieve that goal, it must be a recurring theme, not simply a speech. It must be an extended campaign in the military, not political, sense, requiring repetition and tenacious, overt competition with the ideology of Islamic extremism. Spoken first by our president, it should be echoed by other world leaders. It's what we fight for.

In the short term, the U.S. military has an essential role to play in stopping the tactical advance of ISIS in Syria and Iraq. It's clear that much more U.S. help must be given to Iraqi military forces, moderate Syrian opposition forces, and the Kurds - including the deployment of a limited number of U.S. special operations forces, air controllers, and communications and logistics specialists. Boots on the ground. But strategic victory for the United States and our allies will come only when it is undeniably clear that we are fighting for a worthy cause - and our ISIS adversaries are not.

It's now time to launch a coordinated attack upon the ISIS center of gravity - the misplaced idealism and motivation of its recruits.