WASHINGTON, D.C. – What’s one of the biggest threats to national security that neither presidential candidates are addressing? According to economist Roger Bate, it’s terrorist financing via illicit tobacco, The Daily Caller reports. While both Republican nominee Donald Trump and Democratic nominee Hillary Clinton have promised to protect the country from terrorism, they have yet to speak out against terrorists using the sale of contraband cigarettes and other tobacco products to fund their activities.

“Political debates become very simplistic. To discuss terror financing in and of itself is complicated because you’re not talking about the activity, you’re talking about the financiers of it,” said Bate, an American Enterprise Institute Visiting Scholar.

He acknowledges the complex issue illicit tobacco presents, because “the lines of financing, the movement of products across borders, the cash transactions, even the bank accounts are very hard to trace,” he said. But that doesn’t change the fact that terrorist groups, such as Hamas, Hezbollah and the Pakistani Taliban, all receive money from contraband tobacco, according to a report from the Center for Terrorism Analysis.

The United States founded the Interagency Working Group to Combat Illicit Tobacco last year, which also found links between contraband tobacco and terrorist organizations. “I think it’s an interesting aspect that probably half a mile from where the [first presidential] debate [between Trump and Clinton] was held, there was probably someone smoking an illicit cigarette, which is helping to finance the organizations that one of those two will end up having to tackle as president. And they aren’t even thinking about that at the moment,” Bate said.