Fighters with the Democratic Forces of Syria relax after taking control of Syrian territory from Islamic State militants on Nov. 14. (Rodi Said/Reuters)

James F. Jeffrey, a former ambassador to Iraq, Turkey and Albania, and deputy national security adviser, is a fellow at the Washington Institute.

The horrific Paris attacks , following a likely Islamic State bombing of a Russian airliner in the Sinai and coming in the midst of the crises emanating from the linked conflicts in Iraq and Syria, demand an answer to this question: When will the United States realize that it urgently needs to use real military force to defeat the Islamic State threat?

After almost 18 months of the Obama administration’s half-measures, it’s obvious that defeat of the Islamic State is not going to happen absent a first-class, mobile ground force being launched to mate with overwhelming air power. That ground force does not have to be large — the main U.S. assault force in the largest battle of the second Iraq war, Fallujah in 2004, counted only seven to eight battalions, with reinforcement and support, for a total of 7,000 to 8,000 troops. Nor does it have to be all American. French and other experienced Western troops could complement U.S. forces, as could effective Iraqi and Syrian formations. But without U.S. ground forces, none of this will take place. The Islamic State will hold together its “state,” and its counterattacks — as well as Iranian-Russian exploitation of the Islamic State for their own aggression — will destabilize much of Eurasia and expose the United States again to mass terrorist attacks.

The fact that, even after last week’s Paris attacks, the administration, U.S. presidential candidates and outside experts generally did not embrace this new reality is striking. Former NATO commander James Stavrides and Ohio Gov. John Kasich, a leading establishment figure in the Republican presidential field, urged NATO to take charge of the anti-Islamic State campaign. Other Republican candidates suggested more effective air strikes, and Democratic presidential front-runner Hillary Clinton essentially argued for an expanded version of the current U.S. strategy before adding, “It cannot be an American fight.” Only Sen. Lindsey Graham (R-S.C.) out of the large field of candidates has pressed for significant conventional U.S. ground forces.

Why isn’t the obvious — a traditional military operation — getting serious discussion? In part it’s because of this administration’s “no military solution for anything” mantra, and in part it’s because many Americans, not to speak of our European allies (the British Parliament just opted out of air operations over Syria), consider military operations, and especially ground military operations, in the Middle East to be counterproductive at best and disasters in the making at worst.

President Obama made remarks and answered questions at the G-20 summit in Turkey on Nov. 13. Here's what he said about the path forward fighting the Islamic State, welcoming Muslims and protecting Syrian refugees. (AP)

Even before the Paris attacks, polls showed that a large majority of Americans were disillusioned with the administration’s campaign against the Islamic State and recognized Islamic militancy as a dangerous threat, but more than half still opposed the use of U.S. ground troops. This mind-set was greatly strengthened by the struggles of our ground forces in the Iraq and Afghanistan wars, but its roots lie in the failed interventions in Somalia, Beirut and, of course, Vietnam.

But that mind-set ignores the reality behind these failures. All of these were interventions in civil wars or counterinsurgencies, committing conventional U.S. forces to solving interminable social conflicts and nation-building. That’s not what a rapid takedown of the Islamic States’s quasi-conventional force would require.

A second criticism is that use of ground forces requires convincing, detailed answers to the “day after” questions regarding how to organize large geographic areas, provide security to liberated populations and secure hope for a better future as an alternative to extremism. That is true, but however one responds to those questions, the answer must not include Western troops as an occupying force. Moreover, while figuring out the “day after” might be difficult and implementing any solutions costly, it likely would be easier and less costly than dealing long-term with an Islamic State “state.”

Another argument against U.S. ground troops is a possible alternative: truly serious, industrial-strength U.S. air power and an advisory effort linked to local ground troops, with liberal rules of engagement and forward-deployed U.S. Special Operations forces. While such approaches worked in Afghanistan in 2001, northern Iraq in 2003, Basra in 2008 and Kunduz a month ago, they have not really been tried against the Islamic State. The problem, however, is that we no longer have the time to see if such a suboptimal approach might work, nor do we have sufficient effective local partners. The various Kurdish elements, Iraqi security forces, Sunni tribes, Shiite militias and Syrian resistance fighters on the ground have no common loyalty; many of them confront one another as often as they do the Islamic State. We simply cannot resolve these issues in the time necessary to make this group the primary offensive force.

Finally, the imperative to avoid U.S. casualties usually ends debates about ground troops. While short, crisp offensive operations usually generate relatively limited losses, the truth is that no one can predict casualty levels, and any combat deaths are a tragedy and political risk. But we need to be honest. The Syrian civil war has generated millions of refugees and hundreds of thousands of civilian dead. The Islamic State itself has taken tens of thousands of innocent lives in the region, and now hundreds more civilian lives in Turkey, Egypt, Lebanon and France. At what point does such a growing river of gore justify risking American lives?