Yes, SoS Clinton did mention reauthorizing the Assault Weapons Ban (as did AG Holder) and by most accounts they were told to stop talking about by their boss. Obama once campaigned on reauthorizing the AWB, but has stayed away from it since being elected.
The true number of US guns confiscated in Mexico is far less that you say.
Fox News (yes, that Fox news) put the rate of US firearms confiscated in Mexico at 17%.
http://www.foxnews.com/politics/2009/04/02/myth-percent-small-fraction-guns-mexico-come/But even FactCheck (Funded by the anti-gun organization the Annenberg Foundation) put the number at 34%.
http://www.factcheck.org/2009/04/counting-mexicos-guns/You may say that that is still a lot of US guns and I agree. But if every US gun was kept in the US, there would still be plenty of guns for drug runners to kill each other. We should stop that flow of guns as best we can, but without violating the 2nd Amendment Rights of US citizens.
Its not even clear if one life would be saved in Mexico or anywhere if the AWB was reauthorized. Its not like a criminal or Mexican drug runner says, "oh no, I can't get an semi-auto AK-style rifle with a flash hider so I won't kill anyone." They'll simple use a different gun -- maybe an semi-auto AK-style rifle without a flash hider.
I get it Sabina1, you're concerned. I am too, but I will not allow any US contribution to Mexico's massive drug wars to be used as a reason for violating US civil rights. And woe to any US politician who does.