In testimony before the House Foreign Affairs Committee on Tuesday, George Washington University terrorism expert Seamus Hughes told Congress that the U.S. should pay close attention to the recent spate of ISIS attacks in Europe if we want to be prepared domestically.

“Until recently, IS operated a relative safe haven from which it could plot and plan attacks. Despite its recent territorial losses, it continues to maintain a cadre of sympathizers who feel an obligation to help the beleaguered Caliphate,” Hughes said. “This is one of the main factors that explain the wave of attacks, both thwarted and successful, that have hit Europe and the United States in recent months.”

Hughes pressed the committee to understand that while ISIS was weakening on the battlefield, the fact that they had conducted more than 50 terrorist attacks in Europe and North America since 2014 was not to be overlooked. He also warned that while refugees and asylum seekers carried out some of these attacks, the vast majority were conducted by citizens of the country in which the attack occurred. He said that the U.S. could be thankful not to harbor as many homegrown terrorist networks as our allies across the pond.

“Unlike Europe, the United States does not seem to possess extensive homegrown militant organizations that can provide in-person ideological and logistical support to individuals attracted to IS,” he said. “In contrast, many European countries have militant Salafist organizations that provide individuals undergoing the radicalization process with ideological underpinnings and, in many cases, also with concrete help that facilitates their travel to Syria or Iraq.”

Nevertheless, Hughes said, that was no reason for the U.S. to let down its guard, seeing as how ISIS had grown very adept at using the internet to radicalize and organize their followers from afar. He pointed out that 19 out of 38 ISIS-affiliated plots in Europe between 2014 and 2016 involved online collaboration and instruction of some form.

In a nutshell, this simply means that we have to be vigilant. And thankfully, we seem to finally have an administration in the Executive Branch that isn’t going to pretend that domestic Islamic terrorism is something we don’t have to worry about. Because that’s just the kind of attitude ISIS and others are counting on. No one was thinking very seriously about Islamic terrorism before 2001. That was just something that happened in the Middle East, save for the occasional aberration like the original World Trade Center bombing. We can’t afford to slip back into that kind of thinking, either through complacency or political correctness. Let’s be grateful that Europe’s problems are not our own, but let’s also make sure that they don’t become so.