FBI Director James Comey testified before the Senate Homeland Security and Governmental Affairs Committee Tuesday and predicted ISIS terrorists would eventually seek to disperse to other countries to carry out terror attacks. The Associated Press reports:

Comey said the U.S. remains extremely concerned that violent extremists will eventually flow out of Syria and Iraq and into other countries in hopes of committing attacks.

The number of Americans traveling to Syria to fight alongside the Islamic State group has slowed to a trickle in the last year, but as the so-called caliphate becomes “crushed,” many militants from Western nations who are already there will stream out of the region and create new security threats.

“There will be a terrorist diaspora sometime in the next two to five years like we’ve never seen before,” Comey said.

Senator Ron Johnson, chairman of the committee, framed the threat of more attacks on U.S. soil as “significant.” His opening remarks today were published on the committee’s website:

Over the past year, Americans have suffered attacks inspired by Islamic Terrorism in San Bernardino, Orlando, Columbus, Philadelphia, and—most recently, the vicious attack in St. Cloud, Minnesota, and the bombings in New York and New Jersey.

In all, Islamic extremist terrorist have killed 63 people on U.S. soil since our committee last held its annual hearing to consider threats to the homeland and heard testimony from the heads of the FBI, DHS, and National Counterterrorism Center.  And this does not count the horrific attacks that occurred in Paris, Brussels, and elsewhere across Europe, Africa, and the Middle East…

As Chairman of this Committee, through our hearings and oversight work, I have investigated vulnerabilities in our border, aviation, maritime, visa, cyber, and critical infrastructure security, and where possible I have worked on bipartisan legislation to address these threats.

Here is what I have learned about our nation’s vulnerabilities:

Our borders are not secure.

I am concerned that our system for vetting people coming to this country is not air tight, allowing potential adversaries to enter the country.

Last year a congressional report estimated 250 Americans had left the country to fight with ISIS and concluded that about 85% of them were successful in joining up with the terror group. The situation is much worse in Europe where approximately 6,000 people are believed to have joined ISIS, primarily from the UK, France and Germany.

Sen. Johnson did not read his full statement into the record this morning but did touch on the same themes: