The Paris terror attacks have political leaders worried — and for good reason.
With thousands of miles of border to police, cities full of millions of people, and a virtually uncountable number of electronic messages flying around the world every day, trying to stop a handful of terrorists from committing random acts of violence may be a nearly impossible task.
The gravity of that challenge was clear when top lawmakers on the Senate Intelligence committee emerged from a closed door, classified briefing on Tuesday and talked to reporters about their concerns.
Here's what's keeping lawmakers and intelligence officials up at night:
The Visa Waiver Program
America's nearly 30-year-old visa waiver program helps bring nearly 20 million people from 38 countries — most of them in Europe — to the U.S. ever year with less stringent screening.
Proponents — including lawmakers whose states rely heavily on tourism and the business sector — argue the program is critical to the economy and have pushed for an expansion. Critics have said the program leaves the nation vulnerable to attack from those who trek to ISIS-run terrorist training camps in other countries, head back to Europe and then use the program to come to America.
Experts ranging from CIA Director John Brennan to Sen. Richard Burr, R-N.C. the chairman of the Senate Intelligence committee and California Democrat Sen. Diane Feinstein, the committee's ranking member have expressed concern that the program makes it harder to track would-be terrorists.
"I happen to agree that the visa waiver is the easiest because somebody that goes to fight in France, a visa waiver country, comes back to his country and then he decides he wants to come to California," Feinstein said on Tuesday after a classified briefing on the Paris attacks. "So we need to look at that and explore what the options are, and how to make prudent changes that don't impact our economy dramatically but do offer a significant measure of protection."
One of the most unnerving aspects of the attacks in Paris is that the terrorist targeted so-called "soft targets" such as a concert hall, a soccer match, a bar and a restaurant.
U.S. officials are keenly aware that similar sites in America are vulnerable.
In the nation's capital, officials are beefing up security on the city's subway system and around monuments and memorials, which are big tourist attractions after a propaganda video which purported to be from ISIS was released containing a threat to carry out a similar attack in Washington, D.C.
In response, one school district in Maryland canceled planned field trips to the city. And four people were removed from a Spirit airlines flight on Tuesday as they prepared to take off from Baltimore, after a passenger said one of them appeared to be watching an ISIS video on a cell phone. There were no arrests.
Still, lawmakers and those in the intelligence community worry about attacks on "soft targets".
"It's one thing to hit a building, a building is one thing. It's another thing to hit a soft target. To walk into restaurants where people are having a Friday night dinner, to kill everybody you can kill. To go into a concert hall, do the same thing," Feinstein said on Tuesday in pointed comments after the classified briefing. "So what ISIL used is the soft target. And of course, this is all over television, it's going constantly, and I think it's causing a great deal of alarm among people who want their government to keep them safe, and we want to keep people safe, and only good intelligence is going to keep people safe."
In an address to the State Department's Overseas Security Advisory Council, Secretary John Kerry acknowledged those concerns.
"Since Friday night, there has been a great deal of discussion about so-called soft targets — cafes, restaurants, sporting events, a concert venue, soccer stadium, and so forth — the types of places that you wouldn't automatically expect to be a prime target for a global terrorist organization," Kerry said. "…these targets are viewed as anonymous destinations, chosen almost at random — you can go on Google Map and pick spots and map it out pretty easily these days. And the ultimate purpose of those attacks is to do what the name 'terrorist' implies — to sow terror, to scare everybody. Shopping malls, a restaurant — anywhere. The idea is to make us believe that we are always going to be in such grave and imminent danger that we actually have to stop what we're doing and change our choices and change our way of life."
Encrypted Apps and Communication
One of the intelligence community's biggest fears is that terrorists are plotting right under their noses, but that the spies and agents at the NSA, FBI, CIA and other agencies don't have the tools they need to see their communications in today's high-tech world. That fear has was only made worse after Edward Snowden's revelations caused the American public to start paying more attention to who and when strangers — whether that be hackers, companies, or analysts at the NSA — can see their information.
In the aftermath of the terrorist attacks in Paris, law enforcement officials and politicians on both sides of the Atlantic voiced their concerns that popular encrypted messaging apps like WhatsApp, which is owned by Facebook, and Apple's iMessage could be used by radicalists to talk to one another. There has been no evidence publicly reported linking the use of these or similar services to the attack — but law enforcement has been opposed to encryption for years, with tech companies generally pushing back.
At a forum on Monday, CIA Director John Brennan said that in recent years there have been "unauthorized disclosures" and "a lot of handwringing" that he says have made it harder to find terrorists where they're talking to one another.
"And I do hope that this is going to be a wake-up call, particularly in areas of Europe where I think there has been a misrepresentation of what the intelligence security services are doing by some quarters that are designed to undercut those capabilities," Brennan said.
And while the intelligence services are asking for an extra tool that they say would help protect Americans, not everyone's buying it. Tech companies are taking a stance that they say protects civil liberties — but also just makes good business sense as they try to keep trust and security in a global marketplace. Fourteen top cryptographers and computer scientists put out a paper in July examining government ideas around how to share encrypted communications, and found there's no way to do it without putting systems at risk to malicious hackers.
"I view encryption like many view the 2nd amendment," Mark Cuban, entrepreneur and panelist on CNBC's 'Shark Tank' said in a post on his Cyber Dust messaging app. "Encryption is a fundamental underpinning of the freedom of speech."