President Obama made remarks and answered questions at the G-20 summit in Turkey on Nov. 13. Here's what he said about the path forward fighting the Islamic State, welcoming Muslims and protecting Syrian refugees. (AP)

The carnage of the Paris attacks and the largely stalemated war in Iraq and Syria have prompted heavy criticism of President Obama’s handling of the fight against the Islamic State over the past three years.

The questions came in waves Monday at the Group of 20 summit in Antalya, Turkey: Hadn’t Obama underestimated the threat posed by the Islamic State? Wasn’t it time for a new and more aggressive attack plan? Did he really understand the group well enough to defeat it and protect the United States?

“All right,” Obama replied to the last question, his tone betraying utter indignation. “So this is a variation on the same question. . . . Let me try it one last time.”

In response to each of the questions posed by reporters, Obama made his case for a steady and persistent campaign that seeks to gradually shrink the Islamic State’s territory in Iraq and Syria with airstrikes, slowly build up indigenous ground forces and press for renewed diplomatic negotiations to end Syria’s civil war.

The questions reflected concerns following the Paris attacks — which killed 129 people and led France’s president to promise a “merciless” response — that Obama had missed opportunities to defeat the group when it was still gaining strength.

Now Obama is in the unenviable position of championing a strategy that even he admits could take years to work, and could be marked by significant setbacks and more terrorist attacks like those in Paris.

“The strategy that we are putting forward is the strategy that is ultimately going to work,” the president told reporters Monday. “But as I said from the start, it is going to take time.”

The story of how Obama landed on his approach is one of a president who campaigned for reelection on a promise to end America’s wars and came to office with other pressing priorities, such as reaching an agreement that would prevent Iran from acquiring a nuclear weapon.

He was deeply skeptical that U.S. military power could produce lasting political change in the Middle East and heavily influenced by the steep costs and heavy casualties that America suffered in Iraq and Afghanistan to achieve only mixed results.

In the early days of the Syrian civil war, Obama rejected proposals from his top national security advisers at the time, including Secretary of State Hillary Rodham Clinton, Defense Secretary Leon E. Panetta and CIA Director David H. Petraeus, to arm rebels fighting the government of President Bashar al-Assad.

To Obama, the rebels’ chances looked bleak. They were a collection of “former doctors, farmers, [and] pharmacists,” he said, facing off against a well-equipped Syrian military that also had the support of battle-hardened Hezbollah forces.

Early proposals for a no-fly zone that would have grounded Assad’s jets and attack helicopters were also dismissed as too costly. Martin Dempsey, then chairman of the Joint Chiefs of Staff, estimated that maintaining a no-fly zone would cost as much as $1 billion a year and put the U.S. military into direct conflict with Assad and his Iranian backers.

Today, some analysts say Obama underestimated the moderate Syrian forces that were massing against Assad and that might have been able to pick up support from defecting Syrian military troops if they had shown early success.

“These are people who have a motivation to fight for their own survival,” said Brian Katulis, a Middle East analyst with the left-leaning Center for American Progress. “To say they are just a bunch of farmers is too pessimistic a point of view.”

Other analysts have faulted Obama for not heeding intelligence suggesting that radical Islamist fighters — many of whom had gained experience battling U.S. troops in Iraq — were becoming the dominant resistance force in Syria. In early 2014, as Islamic State militants were expanding their reach from Syria into western Iraq, Obama appeared to dismiss them in an interview with the New Yorker as the “jayvee team.”

“The White House has just never taken the jihadist threat seriously,” said Eliot Cohen, a former senior administration official under President George W. Bush and a professor at the Johns Hopkins School of Advanced International Studies. “Do they have a comprehensive plan that really leads to the destruction of the Islamic State in a couple of years? I don’t think they can plausibly say yes.”

Senior White House officials have countered that the president’s critics vastly overestimate the capacity of American military power to stem chaos caused by decades of misrule and the collapse of repressive governments throughout the Middle East.

To illustrate that point, Obama on Monday described the problems of establishing a no-fly zone or a safe area for moderate rebels in northern Syria. Such a measure recently received the support of Clinton, Obama’s former secretary of state and the front-runner for the Democratic presidential nomination.

“Who would come in and who would come out of that safe zone?” Obama asked. “Would it become a magnet for terrorist attacks, and how many personnel would be required” to safeguard it?

Most pointedly, Obama, who has tried to set hard time limits on U.S. military commitments, wondered if American forces would be required to police it indefinitely.

“How it would end?” he asked.

The question is reflective of the president’s logical, measured approach to waging war and the lack of quick or easy options that he believes are available to him.

Ambitious battlefield goals for rolling back the Islamic State have been shelved indefinitely. Early this year, top U.S. military commanders suggested that an operation to retake Mosul, Iraq’s second-largest city, was weeks or perhaps a few months away. Today, senior administration officials say such an operation might not happen before Obama leaves office.

Instead of big battlefield victories, Obama’s strategy relies heavily on indigenous ground forces, backed by U.S. airstrikes, to slowly capture territory from Islamic State fighters. Obama pointed to the recent push by Iraqi Kurdish forces to retake the Iraqi city of Sinjar as proof of the strategy’s potential.

In Syria, plans to train a force of moderate rebels were abandoned after a months-long effort led by the Pentagon produced only five trained fighters. Now the Pentagon is shifting its focus to building up established groups.

It is also hoping that a diplomatic effort, led by Secretary of State John F. Kerry, can produce a temporary cease-fire between the Assad regime and the more moderate rebels — a deal that even Obama admits faces long odds. “There are any number of ways that this latest diplomatic push could falter,” he said.

The net result is a strategy that offers little immediate satisfaction. For now, one of its biggest selling points is that it largely keeps American soldiers and Marines out of harm’s way.

“This is not an abstraction,” Obama said in defense of his approach. “When we send troops in, those troops get injured, they get killed, they’re away from their families. . . . And so, given the fact that there are enormous sacrifices involved in any military action, it’s best that we don’t shoot first and aim later.”