A week after U.S.-led airstrikes in Syria began, lawmakers continued to question President Barack Obama's strategy for defeating the militant group ISIS, which he admitted in a televised interview Sunday was more powerful than the U.S. initially believed.

Echoing sentiments also expressed by James Clapper, the head of U.S. intelligence services, Obama said the government "underestimated what had been taking place in Syria" during its civil war, allowing Syria to become "ground zero for jihadists around the world."

Speaking in a taped interview with CBS' "60 Minutes," Obama said the terrorists were remnants of al Qaeda in Iraq, which after being diminished by U.S. forces "went back underground."

"Over the past couple of years, 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, adding later the U.S. also overrated Iraq's security forces, which were quickly overrun by ISIS when it took over the northern city of Mosul this summer.

The President stressed that the issue in Iraq is not simply a military problem; it's a political one.

"This is America leading the international community to assist a country with whom we have a security partnership with, to make sure that they are able to take care of their business," he told "60 Minutes."

The President added: "If we do our job right and the Iraqis fight, then over time our role can slow down and taper off."

Obama spent much of last week rallying international support for his mission against ISIS at the United Nations, telling leaders there the fighters represent a "network of death" that must be defeated.

An air campaign, which began last week and included coalition support from five Arab nations, continued over the weekend with strikes on the northern Syrian city of Ayn al-Arab, where Kurdish forces have been battling ISIS.

The mission is meant to "degrade and ultimately destroy" ISIS, Obama says. The White House has remained adamant there won't be any U.S. combat forces deployed in Iraq or Syria, though military "advisers" have been sent to Iraq in the hopes of fortifying local security forces.

The President warned the campaign probably won't conclude any time soon.

"There is a cancer that has grown for too long that suggests that it is acceptable to kill innocent people who worship a different God.

"And that kind of extremism, unfortunately, means that we're going to see for some time the possibility that in a whole bunch of different countries, radical groups may spring up -- particularly in countries that are still relatively fragile, where you had sectarian tensions, where you don't have a strong state security apparatus.

"And that's why what we have to do is, rather than play whack-a-mole and send U.S. troops wherever this occurs, we have to build strong partnerships," Obama told "60 Minutes."

Aides to Obama have been careful to underscore that the military operation in the Middle East won't resemble the wars of the past decade, which left many Americans skeptical of intervention abroad.

"We're doing this in a very different way than in the past," Tony Blinken, a deputy national security adviser, said on CNN's "State of the Union" with Candy Crowley.

"We're not sending in hundreds of thousands of American troops," Blinken continued. "We're not spending trillions of American dollars. What we are doing is empowering local actors with some of the huge assets we can bring to this, like our airpower, intelligence, training and equipping, advising and assisting."

The "no boots on the ground" mantra was questioned Sunday by House Speaker John Boehner, who said if local forces aren't trained to battle ISIS quickly enough, U.S. troops would be required.

"Maybe we can get enough of these forces trained and get 'em on the battlefield. But somebody's boots have to be there," the Republican leader said on ABC's "This Week."

Boehner added later that if Obama advanced a new resolution authorizing the military action in Syria, he would be willing to call lawmakers back from the campaign trail to vote on it.

Obama claims he doesn't need Congress' permission for the air campaign under way in Iraq and Syria, citing the 2001 authorization to go after al Qaeda. He has said he would "welcome" Congress showing its support for the mission.

Sen. Chris Murphy, a Democrat from Connecticut, said Sunday an authorization vote would allow lawmakers -- and by turn the American public -- to hear more about long-term plans in Syria.

"I think the reason that we need to have the debate is so that we can get a better explanation as to what the endgame is in Syria," Murphy, who sits on the Foreign Relations Committee, said on "State of the Union."

"In the end, that's the check on a war without end: a Congress speaking for the American people who can put an end date on an authorization for military force or put a limitation, so that you can't use ground troops," he said.

(CNN)