Leading lawmakers identified Belgium as a hotspot for terrorism months ago and are warning that many of the radicalized individuals living there are still able to travel to the United States without first obtaining a visa and undergoing thorough security checks.

Rep. Ron DeSantis (R., Fla.), a member of the House Foreign Affairs Committee, told the Washington Free Beacon Tuesday afternoon that current flaws in the U.S. visa waiver program—which facilities travel to the United States from partner nations including Belgium—have created a loophole that could permit radicalized individuals to legally enter the United States with minimal background checks.

DeSantis is warning of these flaws on the heels of deadly mass terrorist attack in Brussels on Tuesday that has killed at least 30 and wounded hundreds more.

“The visa waiver reform, this is something we have been perusing and the [Obama] administration has brushed us off at every turn,” DeSantis said, explaining that current policy does not mandate more strenuous checks on individuals identified as coming from terrorist hotspots, such as the small Belgian town of Molenbeek, which has emerged as a principal training site for jihadists.