Now that President Barack Obama has finally laid out a strategy to “degrade and destroy” the Islamic State, there are only two (very big) questions that matter:

Is this strategy really necessary?

And can it succeed?

My answer to the first question is a firm “yes,” but to the second a very shaky “maybe.” Yet I believe Obama has no option but to try.

Until the Islamic State in Syria beheaded two American journalists, the president himself didn’t believe the threat merited a comprehensive strategy. In January, he famously dismissed the Islamic State as the JV team of terrorism. Even after Islamic State fighters swept through Western Iraq, he downplayed the near-term threat.

Yet suddenly, Obama has recognized that the Islamic State, “if left unchecked,” could pose a threat to the homeland (whatever the reason for his about-face, he’s reached the correct conclusion). On Wednesday, he presented a “counterterrorism strategy” that would use American airpower against the Islamic State in Iraq ― and, for the first time, in Syria. There would be no “U.S. boots on the ground,” he stressed; Arab allies will do the funding and provide the ground troops.

Yet it’s fair to ask, as many in his Democratic base are doing, why not let Middle East leaders fight their own battles against the Islamic State?

Answer: Without U.S. leadership, they can’t and won’t, which would put the United States at risk.

The Mideast is in free fall. Regimes are crumbling under the pressure of youthful populations enraged by chronic unemployment and official corruption ― and stirred by the Internet. The Bush administration put a match to this tinder by invading Iraq. The Arab Spring revolts revealed that the post-World War I order had become so rotted it was poised to collapse.

But Arab states lacked the capacity to build new political systems. Syria and Iraq have splintered; Egypt is an economic basket case held together by a repressive military; Libya no longer exists as a state; and Arab monarchs in Jordan and the Gulf are struggling to maintain their hold. None of these countries has the institutions or leadership to meet the aspirations of their people, whose hopes have been dashed again.

In this ideological vacuum, radical Islam can flourish ― because it attracts the disaffected and because it will use any level of violence. The Islamic State aims to create a terrorist state where local and foreign jihadis can train to overthrow Mideast regimes and return to wreak havoc in their home countries. Left unchallenged, the group will soon undermine Saudi Arabia and Jordan. It will also inspire and train radical Islamists from Nigeria to Tunisia to Pakistan (where ― take careful note ― jihadis have penetrated society and a weak state and pose a real threat to a nuclear-armed military).

Already, some regional al-Qaida groups are pledging fealty to the Islamic State.

So we may yearn to tell Mideast leaders, “It’s your problem,” but they are too frightened, too divided among themselves, and too lacking in capability or reliable troops to mount a coherent challenge to the Islamic State. Nor is the United Nations ― paralyzed by Russian and Chinese vetoes ― in any position to step in.

Without U.S. leadership, training, and support, Mideast rulers won’t prevent the Islamic State from growing to the point where it threatens the entire region. It is vital to disrupt the group now.

Which brings us to the huge second question: Will Obama’s strategy work?

The most glaring gap in his plans is the prospect of finding the ground troops that can fight the Islamic State in Iraq or Syria, assisted by U.S. air strikes. No question, it would have been far easier to crush the jihadis in Syria two years ago by helping moderate rebels. But by now most of those groups have been crushed between the Assad regime and the Islamic State. Obama’s belated and still vague plans for the Defense Department to train a new “moderate” rebel force are too little, too late.

There are better prospects in Iraq, where the administration can count on Kurdish forces, to whom it should be rushing support directly. Less certain is whether the new Iraqi prime minister, Haider al-Abadi, can reverse the sectarian Shiite ways of his predecessor, Nouri al-Maliki, which alienated many Sunnis to the point where they helped the Islamic State take over western Iraq.

Al-Maliki reneged on promises that were made to Sunni tribes when they fought al-Qaida with U.S. help in the past decade. Persuading them to take up the fight again will not be easy; it will require tough, skilled, and top-level U.S. diplomacy of a sort that has been sorely lacking over the past three years ― when it probably could have prevented the Islamic State’s rise.

At this point, it’s possible there won’t be sufficient ground troops available in Iraq, let alone Syria, to roll the Islamic State back from its territorial gains in the near term. All the more reason for the United States to use airpower to prevent Islamic State expansion in Iraq and disrupt its command structures in Syria. Despite the risks, and the long-term nature of the task, doing less is riskier still.

Until the Middle East emerges from its current disrepair, until Iraqis and Syrians can resolve their sectarian disputes or divide into separate states, the terrain will be fertile for the rise of the Islamic State and other radical movements. In the meantime, the United States cannot afford to stand by while the Islamic State trains militants from all over the world and develops a global network that threatens our homeland.

This is why Obama had to shift gears and finally turn his attention to the Middle East.

By Trudy Rubin

Trudy Rubin is a columnist and editorial board member of the Philadelphia Inquirer. Readers may write to her at trubin@phillynews.com. ― Ed.

(MCT Information Services)