belgium. >> the problem originates in belgium. >> belgium is one of 26 european countries with open borders. but crossing those borders, you can see how easily terrorists can also exploit that freedom. we're now driving from belgium into france. i do have my passpert with me, but i won't actually need it because essentially there's no checkpoint here. it's free and open highway. it's like driving from nebraska into kansas. in fact the only way you can even tell you've moved into another country is because the cellphone carrier changes. so this is belgium's new normal, soldiers and heavily armed police on patrol day and night. even as isis supporters are hidden in plain sight. >> and the most frightening thing, thousands of young