Joint Chiefs of Staff Chairman Gen. Martin Dempsey, right, and Defense Secretary Ashton Carter attend a Senate Armed Services Committee hearing Tuesday. (Win Mcnamee/Getty Images)

IN MAY 2014, President Obama promised a new U.S. effort to train and equip moderate Syrian rebel forces. The next month, the administration asked Congress for $500 million to fund the effort, with the aim of deploying 5,000 U.S.-backed fighters a year for three years. Numerous analysts quickly pointed out two big flaws in the plan: The new force was too small to make a significant difference on Syria’s multi-sided battlefield, and the administration was hamstringing it by insisting that it target only the Islamic State and not the regime of Syrian President Bashar al-Assad. As so often in his handling of Syria, Mr. Obama dismissed proposals for a more robust approach.

Now, once again, the president is reaping the consequences of his half-measures. On Tuesday, Defense Secretary Ashton B. Carter reported the pitiful result of the training program: After a year, he told the Senate Armed Services Committee, just 60 Syrians were enlisted. Meanwhile, Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, testified that Israel and Jordan “very much believe [in] the possibility” that the Assad regime could soon collapse, touching off “a foot race” of al-Qaeda and Islamic State forces “converging on Damascus.”

Since the United States has failed to train or support a moderate Syrian force capable of countering the extremists, it has no ready way to prevent that disaster. “I won’t sit here today and tell you that I have the answer to that,” Gen. Dempsey told the committee.

The latest U.S. failure in Syria is particularly striking because, as Mr. Obama emphasized in an appearance Monday at the Pentagon, the foundation of his policy in Iraq and Syria is to train local forces that the United States can support. The president conceded that “this aspect of our strategy was moving too slowly”; in fact, it has failed in both countries. According to Mr. Carter, the 3,500 U.S. personnel deployed in Iraq since last year had trained just 8,800 Iraqi army and Kurdish militia soldiers. Just 1,300 Sunni tribesmen have been recruited, though Mr. Carter said such Sunni forces were essential to retaking cities captured by the Islamic State.

Administration officials have a penchant for blaming Iraqi and Syrian Sunnis for lacking the “will” to fight, without considering why that might be. A couple of the principal reasons are the product of Mr. Obama’s policies. Sunni leaders don’t trust the United States to defend them against the Iranian-backed Shiite militias that operate in concert with the Iraqi government. They wonder why the White House still refuses to deploy Special Operations forces advisers or tactical air controllers to the front lines with Iraqi units, even though, as Gen. Dempsey testified, that “would make them more capable.”

Syrian Sunni fighters want to join a force that will take on the Assad regime as well as the Islamic State, but the Obama administration won’t even commit to defending the fighters it is training if they are subjected to the regime’s signature “barrel bomb” attacks. “That decision will be faced when we introduce fighters into the field,” Mr. Carter told the Senate panel. Unless Mr. Obama is prepared to make a more decisive commitment to training and defending U.S.-allied forces, there won’t be many of them.