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)

As France reels from a set of Islamic State terrorist attacks in Paris last week that killed scores and wounded hundreds, Americans are wondering whether their own country is any safer.

“That’s an easy one,” said a former senior FBI official who until recently was deeply involved in terrorism operations. “Safer here than there? Yes. We are separated by an ocean. Without a doubt, we are safer here than over there.”

Since Sept. 11, 2001, the U.S. government has spent more than $1 trillion fighting the war on terrorism, making border crossings more secure, detecting plots and expanding the no-fly list from about a dozen people to roughly 47,000.

Tougher post-9/11 terrorism laws also ensure that the FBI and federal prosecutors can charge people with crimes that carry stiff sentences. In the past 18 months, the FBI has charged more than 60 people in connection with the Islamic State. Many could face years in prison if convicted, meaning the FBI won’t have to devote resources to tracking their movements.

America’s suspected ISIS supporters

In Europe, porous borders mean that hundreds of foreign fighters have slipped back into the continent from Iraq and Syria, overwhelming intelligence agencies trying to keep tabs on them. That appears to have been the case in the Paris attacks, where at least four of the possible nine attackers were known to European authorities. Another suspected key player in the plot fought in Syria and later returned to Europe, only to flee back to the Islamic State.

The number of Americans who have traveled to Iraq and Syria — or at least attempted to — is about 250, dramatically less than the estimated 4,500 who have left Europe. FBI officials aren’t taking the threat lightly, but they have expressed confidence that they have those U.S. individuals contained and that the remaining Americans in Syria won’t be returning to this country unless they are in handcuffs.

That assessment is echoed in a new report by the New America Foundation titled “ISIS in the West: The New Faces of Extremism.”

“Tracking the many foreign fighters from Western countries who have gone to Syria and have returned to the West poses a greater challenge, given their larger numbers, than tracking the handful of returning American fighters,” the report says.

But that doesn’t mean the United States is not vulnerable. The FBI, which is charged with fighting terrorism in this country, has struggled at times to keep pace with a metastasizing threat.

Because of limited resources, the FBI must constantly reevaluate which targets are a priority when it comes to closely following top-tier terrorism suspects. “It’s daunting,” said the former senior FBI official, who spoke on the condition of anonymity to discuss the bureau.

What we know so far about who carried out the Paris attacks

Many law enforcement officials also argue that it would be easier to do their jobs if U.S. tech firms made it possible for phones and apps to be wiretapped. It is not yet known whether the plotters of the Paris terrorist attacks used encrypted channels of communication, but experts say it is highly likely that they did.

Cyrus R. Vance Jr., the district attorney for Manhattan, who has been outspoken on how a lack of access to encrypted communications has hindered investigations, is expected to unveil a proposal on this topic Wednesday at a conference in New York. FBI Director James B. Comey also is to appear at the event. Last year, Comey called for legislation on encryption but later backed down when it became clear that Congress was hostile to the idea of aiding government surveillance.

Comey said recently that the FBI has about 900 cases involving homegrown violent extremists in every state. The vast majority of them, FBI officials say, are related to the Islamic State.

These, however, are a fraction of the approximately 10,000 terrorism cases the FBI has opened — many are overseas cases involving crimes against Americans, such as journalist James Foley, who was beheaded last year on video by Mohammed Emwazi, better known as “Jihadi John.” Authorities believe Emwazi was killed in a U.S. drone strike Thursday.

The FBI felt the Islamic State’s reach acutely earlier this year when it had to reassign hundreds of agents from its criminal division to deal with the Islamic State threat across the country.

“We had dozens of people,” Comey said recently at an event in Washington. “We had to find ways to incapacitate them, all popping up going to kill people.” When asked whether the bureau could sustain that pace without additional resources, he expressed doubt.

“If that were the new normal, that would be very stressful,” he said. “It’s a hard time for the bureau. Only on TV is it easy to follow people.”

The FBI is faced with guarding against two types of terrorist scenarios. In one, a plan is developed in the terrorist group’s stronghold in Raqqa, Syria, and foreign fighters, skilled in the use of weapons and explosives, return home and mount a large-scale attack. The FBI has been training with police departments across the country to respond to a terrorist attack similar to the one that took place in Mumbai in 2008, when a team of 10 militants killed 164 people.

Last month, dozens of FBI agents from the Washington field office, Fairfax County, Va., police officers and tactically trained fire department personnel descended on a large shopping mall afterhours at 10 p.m. and played out such an attack until 4 a.m. the next day.

But FBI officials believe that scenario is less likely to happen in the United States.

They say a more probable attack would involve individuals inspired by Islamic State propaganda to act on their own — people Comey has described as “unmoored,” “unpredictable” and “wingnuts.”

That second scenario has already happened. Among the many Americans the FBI has charged, some are accused of plotting — without direction from the Islamic State — to kill U.S. military personnel and detonate bombs in New York City.

The FBI said two men in Boston — including Usaamah Abdullah Rahim, 26 — and a third man in Rhode Island had discussed beheading Pamela Geller, an outspoken critic of Islam. They planned to kill her July 4, the FBI said.

When Rahim decided to act early, the FBI was monitoring his phone.

One of the FBI’s armed mobile surveillance teams confronted the knife-wielding Rahim and killed him.

“Luckily, we were covering that phone,” Comey has said.

In another incident, two Phoenix men, one of whom was under FBI investigation, tried to attack a prophet Muhammad cartoon contest in Garland, Tex., which had been organized by Geller. Both men — Elton Simpson and Nadir Soofi — were killed. Although the FBI did not know of their exact plans, officials say the field office should have reacted more quickly when it learned Simpson might be interested in going to the contest.

An FBI counterterrorism official described Garland as a failure on the front end and a success story on the back end. Given the inflammatory nature of the event, the FBI persuaded local police to increase the number of officers from a handful to more than 40. When Simpson arrived, he was vastly outgunned. Police were ready.

Months after the event, Comey said the bureau still had questions about what happened and the Islamic State’s role in the attack. Simpson had hundreds of exchanges with an Islamic State operative overseas, with the two communicating using end-to-end encryption.

“We don’t know even today what was said between the two of them,” Comey said. “We know they were in direct communication with him the day he left to go kill people in Garland, TX. This is an example of the problem that I call going dark.”

It’s not clear how the attacks in Paris will affect FBI operations in the United States and whether there will be an uptick in cases.

Comey said late last month that the pace had dropped a “little bit” since the summer, and so he moved FBI personnel back to their usual roles in the criminal division. He said that since July 1, the FBI had detected only six U.S. travelers trying to reach the Islamic State’s self-declared caliphate. In the months before, the FBI was seeing far more than that.

Comey speculated that perhaps part of the Islamic State’s message urging Muslims to come to the caliphate was “becoming less effective.”

“Something interesting is going on that I don’t know enough about to tell you about with high confidence,” he said. “Something has happened that has flattened the curve.”

That was before Paris.

Ellen Nakashima and Julie Tate contributed to this report.

Read more:

Experts: Terrorists learning from one another and going after soft targets

From hip-hop to jihad, how the Islamic State became a magnet for converts

Tracking the Islamic State’s rise