By killing dozens of people in Paris on Friday, ISIS showed the world its intention of bringing its terrorism to the West.
President Obama said he saw little reason to change his current approach, which relies on a combination of airstrikes, training of local anti-ISIS forces and cutting off the group's financing — and an aversion to sending ground troops.
"There will be an intensification of the strategy we put forward, but the strategy that we are putting forward is the strategy that ultimately is going to work," Obama said. "But as I said from the start, it is going to take time."
But many analysts say the Paris attacks — and the earlier bombing of Beirut and a Russian tourist plane — prove that the United States' campaign to thwart ISIS in Syria and Iraq is failing.
"Paris changes everything," Republican Congressman Michael McCaul, chairman of the House Homeland Security Committee, told "Meet The Press." "It should galvanize the entire world behind our efforts to defeat and destroy ISIS, not just to contain them."
Which raises the question: if the current effort won't work, then what will?
NBC News asked experts how they thought the United States should move forward.
This is what they said.
The 'slow squeeze'
"In a certain way, I'm sympathetic to the president's desire not to get sucked into the region," said Michael Eisenstadt, director of the military and security studies program at the Washington Institute for Near East Policy. "That's why I subscribe to the slow-squeeze."
That, he said, means a gradual ratcheting-up of airstrikes and involvement of special operations forces on the ground, even if they carry greater risks of casualties to civilians or military members. Doing it slowly allows diplomats to work out political resolutions.
"That's a significant trade-off, but a lot of people are dying because they're under ISIS control already," Eisenstadt said.
The approach would allow the United States and its allies to tout more battlefield victories and seize more territory, which would hurt ISIS' sophisticated recruitment efforts — and give local civilians confidence to oppose the group, Eisenstadt said.
"In order to undermine their appeal, we have to undermine the perception of momentum, and we have failed in that regard."
Michael Leiter, who served as director of the National Counterterrorism Center under Obama and former president George W. Bush, advocates a similar goal, but one he says can be achieved faster by sending a large number of American combat troops into both countries.
"We may not need the same number that we needed when we first went into Iraq," Leiter told "Meet the Press." "But we need more troops to push the Iraqis faster."
He added, "We need more than 50 special operations forces in Syria to take the fight there, and we have to make clear that they don't stand a chance against us."
As things currently stand, he said, "we are basically playing even. And that helps the movement beyond Syria and Iraq see that this is an attractive army to fight for."
Arm the Kurds
In David Phillips' mind, there wouldn't be much of any progress on the ground against ISIS if it weren't for the Kurds of Syria and Iraq.
That is why Phillips, director of the Program on Peace-building and Rights at Columbia University's Institute for the Study of Human Rights, recommends that the United States send more weapons and political support to the Kurds.
"The United States refuses to put boots on the ground, but the Kurds are serving that purpose," Phillips said Tuesday by phone from Iraqi Kurdistan, where he was working to help the locals develop their government and military so the United States and its allies will consider them a viable partner.
"We should be treating them like an army instead of like a tribal militia," he added. "They deserve more."
Special ops 'mayhem'
The attacks on the French and Russians has motivated leaders of those countries to seek ways to join forces, something the United States has been pushing for all along. This potential partnership may extend beyond the ongoing airstrike campaign.
That development excites Malcolm Nance. He's a retired Navy intelligence and counter-terrorism officer who runs TAPSTRI, a nonprofit think tank in upstate New York. He would like to see the United States, Europe and local allies — including the Kurdish peshmerga fighters and Iraq's elite Golden Division — pool their special operations units to create joint strike forces that could conduct quick, clandestine raids on ISIS outposts and destroy the group's transportation and communication routes.
"Wreak mayhem and maraud, and disappear," Nance said.
Such operations have been done frequently in Afghanistan, he said. But for the ISIS campaign Nance sees as a possible model the United States' raid last week in eastern Syria in which ISIS commander Aby Sayyaf was killed and his records of how the group finances its operations.
"The entire narrative of the ISIS would change overnight because we would be all around those guys," Nance said. "And they would have to get on the road to come get us, which would expose them to airpower."
Phyllis Bennis, the director of the New Internationalism Project at the Institute for Policy Studies, just wrote a book about ISIS. It's called "Understanding ISIS and the New Global War on Terror." In it, Bennis presses for an approach that hasn't been given much consideration since Friday's attacks in Paris.
It begins with the Hippocratic oath that physicians take before they start treating people: Do no harm.
Bennis agrees with Obama that the United States should not send troops. But she said the military campaign — airstrikes included — is a complete failure, and actually hurts diplomatic and humanitarian efforts.
"This is a war of vengeance. And wars of vengeance never work," Bennis said in an interview. "Our leaders are supposed to look beyond that. But nobody is even questioning the idea of the airstrikes. The only debate is over ground strikes."
She would like to see Obama, French President Francoise Hollande and other coalition leaders embark immediately on negotiations for a cease-fire. From there, she'd like to see a complete military withdrawal, a blockade of arms into Syria, a huge new influx of humanitarian aid, and a redoubling of efforts to block ISIS' fundraising sources, notably the sale of oil.
After Paris, "There needs to be answers, and people are understandably insistent that there be a response," she said. "But it's never true that the only option is war."