US officials think ISIS will attack America this year
Lt. Gen. Vincent Stewart, director of the Defense Intelligence Agency, told the Senate Armed Services Committee that ISIS (also known as the Islamic State, ISIL, or Daesh) "will probably attempt to conduct additional attacks in Europe, and attempt to direct attacks on the US homeland in 2016."
Director of National Intelligence James Clapper told the committee that ISIS is "taking advantage of the torrent of migrants to insert operatives into that flow" and warned that the group is "pretty skilled at phony passports so they can travel ostensibly as legitimate travelers."
"As we saw in the November Paris attacks," in which ISIS operatives trained in the Middle East killed 130 people across the city in a single night, "returning foreign fighters with firsthand battlefield experience pose a dangerous operational threat," Clapper said.
"Although the US is a much harder target than Europe, ISIL's leaders are determined to strike the US homeland beyond inspiring homegrown violent extremists attacks."
However, some experts have thrown cold water on these alarming predictions.
Christopher Smith, an adjunct professor of national security studies at Georgetown University, said concerns about highly trained ISIS operatives getting into the US are likely overblown. He said this week that ISIS is more likely to try to radicalize people who are already in the US rather than send operatives overseas.
"It's a lower-cost strategy for ISIS and they don't need to have a major event to have an effect, it's sufficient for them to have a moderate number of small events that are difficult for people to anticipate," Smith, who testified in front of the House subcommittee on terrorism this week, told Business Insider.
And because anyone with an internet connection can find ISIS propaganda online, it's easy for people with no formal connections to terrorist groups to become radicalized but fly under the radar of US law enforcement. People coming into the US who have traveled to conflict zones overseas, however, are going to look more suspicious.
It would also take highly trained ISIS operatives out of the group's territory in the Middle East, where they could be useful.
"Throwing a set of operatives at the US border, you're taking high-value people and throwing them at a hard target," Smith said. "It would show a level of desperation on their part because it'd show they're willing to make an investment that they haven't been willing to make to date."
Motivating radicalized "lone wolves" in the US will likely be of lower impact for ISIS - to pull off a Paris-style attack with high casualty counts, it takes sophisticated planning and a group of trained terrorists - but it's also more likely to be successful.
"It's low cost, it's easier to do, it has a higher likelihood of success and a lower likelihood of discovery," Smith said.
But Smith did caution that as ISIS loses ground in the Middle East amid a campaign of US-led airstrikes and local ground offensives, it will look to strike external targets in the West, including the US.
"When you're losing, you try to get your adversary to stop beating you," Smith said. "And one of the ways to do that is to turn the tables on your adversary and hit them."
Peter Bergen, a journalist and national security analyst who recently wrote the book "United States of Jihad: Investigating America's Homegrown Terrorists," made a similar assessment.
"I think it's quite unlikely that there would be a Paris-style attack in the United States," Bergen told Business Insider.
"They almost all trained in Syria, there were probably a couple of dozen people in a support network in both France and Belgium. We just don't have that here. And we've had a number of people, Americans, who've gone to join ISIS; usually it's a one-way ticket."
The ocean between the US and the Middle East and Europe also helps.
"We're protected by our geography," Bergen said. "You can drive from Paris to Damascus; you can't drive from Damascus to New York City."
Europe is also dealing with a massive refugee crisis that the US has been largely insulated from. And American Muslims are generally more integrated into society than European Muslims, many of whom are confined to housing projects on the outskirts of big cities. The discrimination they face might motivate some to turn to radical Islamist groups.
"... The profile of a terrorist in Europe now amongst the Muslim population is they are very disadvantaged, they come out of a criminal background, they often meet in prison and are radicalized in prison. And we're not seeing that in the United States because American Muslims don't live in ghettos, their average income is the same as the average American, the average education is the same."
Still, ISIS has been steadily ramping up attacks against the West, and the US is a prime target.
"Sunni violent extremists will probably continually plot against US interests overseas. A smaller number will attempt to overcome the logistical challenges associated with conducting attacks on the US homeland."
And Clapper did acknowledge that the greatest threat the US likely faces is from "lone wolves" who might never have visited ISIS territory but still could act in the interest of the group.
"The perceived success of attacks by [homegrown violent extremists] in Europe and North America, such as those in Chattanooga and San Bernardino, might motivate others to replicate opportunistic attacks with little or no warning, diminishing our ability to detect terrorist operational planning and readiness," Clapper said.
"ISIL involvement in homeland attack activity will probably continue to involve those who draw inspiration from the group's highly sophisticated media without direct guidance from ISIL leadership and individuals in the United States or abroad who receive direct guidance and specific direction from ISIL members or leaders."