As the Middle East bloodily unravels, Barack Obama’s defenders have been offering a two-part argument. The worsening mess, they say, is not his fault; and, in any case, no one is offering an alternative to his strategy.

“U.S. policy is not the main source of this change and the U.S. has no good options for dealing with it,” wrote Philip Gordon, Obama’s recently departed National Security Council chief for the Middle East, in Politico last week. Argued former NSC and Pentagon official Derek Chollet in The Post: “When one peels away the rhetoric, what (Republicans) advocate largely resembles the policies of the president they claim is such a failure.”

There is some truth in this. Of course the United States is not the main cause of chaos in Iraq, Syria and much of the rest of the Middle East; and while Republican presidential candidates have unanimously condemned Obama’s “weakness,” none are proposing a radical change of policy.

On the right, Sen. Lindsey Graham, R-S.C., would increase the number of U.S. troops training the Iraqi army from 3,000 to 10,000; at the other extreme, Sen. Rand Paul, R-Ky., rules out U.S. ground forces. But both support the basic idea that the United States should defeat the Islamic State by supporting Iraqi and other forces against it, rather than by launching another major ground war, or dismiss the threat altogether.

All of this, however, obscures the point. The problem with Obama’s Mideast defense, as with so much of his foreign policy, is that it ignores the moderate, pragmatic options between his minimalism and all-out war. No, Obama is not exclusively responsible for the Islamic State’s capture of Mosul last summer, or Ramadi last month, but U.S. steps far short of another 2003-style invasion could have prevented it. Those incremental measures could still turn the campaign against the Islamic State from a stalemate to a success — and prevent an Iran that soon may be freed from sanctions from gaining hegemony over the region.

Start with the Iraqi army, which everyone agrees must take the lead in recapturing the big cities held by the Islamic State. The U.S. troops retraining the army now operate only at the top — at the level of divisions — rather than pairing up with smaller units and deploying with them to the front lines. The latter is the technique that proved to be effective in U.S. operations with the Iraqi army before 2010 and with the Afghan army more recently. But Obama has insisted on the more restricted approach for political reasons: to lower the risk of U.S. casualties and the appearance that U.S. soldiers are engaged in combat operations.

It’s become obvious that the limitation is crippling. U.S. advisers are unable to bolster Iraqi units when they come under attack or to call in airstrikes by U.S. planes. Daily airstrikes against the Islamic State are one-sixth of what they were in the first campaign against the Taliban in 2001-2002, which resembled the current war against the Islamic State. According to Sen. John McCain, R-Ariz., three-quarters of planes return to base without using their weapons because of an inability to locate targets.

A second problem is the failure to provide pro-U.S. forces with adequate weapons and training. For a year, while the Islamic State has expanded and Iran has heaped tanks, artillery and other arms on Iraqi Shiite militias, Obama has refused requests for U.S. weapons from Kurdish militia as well as Iraqi Sunni tribes. The White House insists that the arms must go through the Iraqi government, but that government, under Iran’s sway, has repeatedly failed to pass them along.

Because the Kurds and Sunnis remain weak, the United States is forced to support operations by Iran’s proxies, including militias it has designated as terrorist organizations. Obama could check Iran and strengthen the attack on the Islamic State by directly providing the needed weapons. But he doesn’t.

The president’s biggest failing remains his non-fulfillment even of his own limited plans for Syria. The White House announced its intention to arm and train 15,000 Syrian rebels on June 26, 2014; one year later, just 140 have been recruited. For years, some officials have pressed for the creation, with Turkey’s help, of a safe zone in Syria where the rebels and an alternative government could gather, safe from aerial attack by the regime of Bashar al-Assad. Obama still refuses, while offering no other strategy for preventing the Islamic State’s further expansion or removing the Assad regime.

Repairing these weaknesses would almost certainly change the balance of forces on the ground, strengthen U.S. allies and weaken Iran. The Mideast wars may continue for years, but the United States could do a lot more to shape their eventual outcome. Insisting on American powerlessness, and the absence of alternatives, isn’t a remedy.

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