This transcript from CBS is from an interview between Bob Schieffer and President Obama. It does not answer the question, but definitely poses it:
16:53:23:00 Let me ask you about (COUGHING) something closer to home and that is Mexico. You talked about sending more aid to the Mexican government. But things down there are really serious, as you well know. It’s my understanding that 90 percent of the guns that they’re getting down in Mexico are coming from the United States. We don’t seem to be doing a very good job of– cutting off the gun flow. Do you need any kind of– legislative help on that front? Have you, for example, thought about– asking Congress to reinstate the– ban on assault weapons?
16:53:53:00 Well, I think the main thing we need is better enforcement. And so– this week we put forward a comprehensive initiative to assist those– border regions that are being threatened by– by these drug cartels– to provide assistance to the Mexican government to make sure that on our side of the border we’ve got more personnel, more surveillance equipment.