In the aftermath of Tuesday’s terror attacks in Brussels that left at least 30 dead, conservatives in Congress say that addressing border security is the key to ensuring terrorists don’t end up in the United States.

In response to a question about how the country can improve its intelligence capabilities, lawmakers attending the monthly event Conversations with Conservatives pointed to securing the border as a way to stop terrorists from striking or entering the United States.

“We’ve been saying over and over this isn’t about dealing with Mexico. This is dealing with national security,” Rep. Matt Salmon, R-Ariz., told reporters Tuesday. “This dialogue about immigration and all the people that are coming across the border, it doesn’t do justice to the fact that it is a serious security breach, and if we’re going to take seriously dealing with ISIS and other terrorist groups across the globe, then we have to secure the border.”

Rep. Dave Brat, R-Va., criticized Immigration and Customs Enforcement, specifically, for failing to enforce the laws on the books, particularly when it comes to illegal immigrants who appear in court, are released, and don’t show up again.