Islamic State threat 'underestimated' by US: Obama

President Barack Obama acknowledged that U.S. intelligence agencies underestimated the threat from Islamic State militants in the Middle East and overestimated the ability and will of Iraq's army to fight such extremists.

Obama described the U.S. intelligence assessments in response to a question during a CBS "60 Minutes" interview that aired Sunday, in which he also conceded that the U.S. led military campaign against that group and an al-Qaida affiliate in Syria was helping Syrian dictator Bashar Assad, a man the U.N. has accused of war crimes.

But Obama said he had no choice but to order U.S. air strikes on Assad's enemies, the Islamic State and the Khorasan Group because, he said, "those folks could kill Americans."

The Islamic State group, which derived from but has broken with al-Qaida, has taken control of large sections of Iraq and Syria. The Khorasan Group is a cell of militants that the U.S. says is plotting attacks against the West in cooperation with the Nusra front, Syria's al-Qaida affiliate.

Obama was asked how Islamic State fighters had come to control so much territory in Syria and Iraq and whether it was a surprise to him. The president said that during the Iraq war, U.S. military forces with the help of Iraq's Sunni tribes were able to quash al-Qaida fighters, who went "back underground."

"During the chaos of the Syrian civil war, where essentially you have huge swaths of the country that are completely ungoverned, they were able to reconstitute themselves and take advantage of that chaos," Obama said, according to an excerpt release before the show aired.

He noted that his director of national intelligence, James Clapper, has acknowledged that the U.S. "underestimated what had been taking place in Syria." Obama also said it was "absolutely true" that the U.S. overestimated the ability and will of the Iraqi army.

Both the Islamic State group and the Khorasan Group have been targeted by U.S. airstrikes in recent days; together they constitute the most significant military opposition to Assad, whose government the U.S. would like to see gone.

On the fact that the U.S.-led military campaign had worked to Assad's benefit, Obama said, "I recognize the contradiction," but added: "We are not going to stabilize Syria under the rule of Assad," whose government has committed "terrible atrocities."

Republican Sen. John McCain, who lost the presidential election to Obama in 2008 and has been a frequent critic on foreign policy, said Monday that the administration had miscalculated the necessity for the United States to keep a residual force of troops in Iraq after the war there ended.

"We predicted exactly what would happen. ... It's like watching a train wreck," McCain said on CNN. "A residual force would have stabilized the situation. It is a direct result of our failure to leave a residual force there."

The United States and the government of then-Prime Minister Nouri al-Maliki could not come to terms on agreement providing a residual force of American troops to remain in Iraq.

Obama said his first priority now is degrading the extremists who are threatening Iraq and the West. To defeat them, he acknowledged, would require a competent local ground force, something no analyst predicts will surface any time soon in Syria, despite U.S. plans to arm and train "moderate" rebels. The U.S. has said it would not cooperate with the Assad government.

"Right now, we've got a campaign plan that has a strong chance for success in Iraq," the president said. "Syria is a more challenging situation."

House of Representatives Speaker John Boehner questioned Obama's strategy to destroy the Islamic State group. Boehner said Sunday on ABC's "This Week" that the U.S. may have "no choice" but to send in American troops if the mix of U.S.-led airstrikes and a ground campaign reliant on Iraqi forces, Kurdish fighters and moderate Syrian rebels fails to achieve that goal.

"These are barbarians. They intend to kill us," Boehner said. "And if we don't destroy them first, we're going to pay the price."

Obama, though, made clear he has no interest in a major U.S. ground presence beyond the 1,600 American advisers and special operations troops he already has ordered to Iraq.

"We are assisting Iraq in a very real battle that's taking place on their soil, with their troops," the president said. "This is not America against ISIL," he said, using an alternative name for the Islamic State group. "This is America leading the international community to assist a country with whom we have a security partnership."

Only the U.S. can lead such a campaign, Obama said. "We have capacity no one else has. Our military is the best in the history of the world. And when trouble comes up anywhere in the world, they don't call Beijing. They don't call Moscow. They call us."