President Barack Obama is renewing his call for Congress to authorize another $500 million for pro-Western rebels in Syria. There is growing pressure on the president to combat ISIS, also known as the extremist terrorist group Islamic State, and to help topple the regime of Syrian president Bashar al-Assad.

But what does $500 million buy in this scenario?

When the president first proposed the aid back in June, the money was expected to train and arm 2,300–2,500 Syrian rebels. That’s less aid than Assad’s opposition wants.

“You’re talking about everything from Kalashnikovs to rocket launchers and grenade launchers,” says Andrew Tabler, a Syrian expert at the Washington Institute for Near East Policy. “The real question is does that include anything close to an anti-aircraft weapon?”

The administration is worried about funding those kinds of weapons because they can easily fall into the wrong hands. A new report indicates that anti-tank weapons once owned by Syrian rebels are now in the hands of Islamic State militants.

Haim Malka, deputy director of the Middle East program at the Center for Strategic and International Studies, says the problem is figuring out exactly which groups to give money to.

“Many of them may share U.S. objectives of fighting the Islamic State or fighting the Assad regime today, but we’re not sure exactly what their agenda is going to be tomorrow.”

Tabler of the Washington Institute for Near East Policy predicts the U.S. will get more deeply involved in the Syrian conflict.

“We were naïve to think we could get out of it,” says Tabler. “What happens in the Middle East doesn’t stay in the Middle East.”