...
What is going to happen then? Will the Trump administration star raiding the weapons industry of the US to prevent those weapons bein sent to the terrorists?
Actually, that is nothing new and has continuously been happening with industrialized countries, which are at the same time the biggest producers and exporters of fire arms on the planet. I remember a documentary film from Germany which traced those weapons being used in African uprisings and guerilla combatants back to their manufacture sites within the German republic.
It has been the same when comes to Mexican cartels and weapons manufacturers in the USA.
It does not matter who the president is or whether those cartels are labeled as terrorists or not, money and weapons are going to try to continue to flow in the underground market for those weapons. Trump will do nothing, as actions against weapons manufacturers would be legally challenged and it may even within the interest of those companies to continue to supply weapons to cartels and other criminal groups beyond the southern border.
It is not really "nothing". I mean, it is nothing if you recognise that US is arming the cartels with high power weapons, such as assault rifles and machine guns, providing them with funds comming from the drug consumption in the US but at the same time you insist that Mexicans are criminals. I am not sure if make myself clear.
As understood, Hispo isn't actually stating that the USA government is directly arming these cartels but that the US has been a channel through which weapons could be acquired by moat of these cartels and this he is generally pointing as a something found with industrialised countries of the world.
It's just that there's hardly anyway the black market for guns exchanging hands with money can entirely be eliminated since most of these highly profiled cartels are somewhat sponsored  by some corrupt government officials serving as benefactors.
I did not say the government, but you could argue that the Mexican government isn't sending drugs over the border either.
The weapons sent to Mexico are not legal exports, they are bought easily by US people who can pretty much access a gun in the supermarket and probably with less requisites than buying alcohol and then selling them to the cartels.
The problem of Mexico is having the US nearby buying drugs in ridiculous ammounts. It is that money that is being used to corrupt the governments or more likely to threaten the right people into submission.
What better way to take down the Mexican Government... which was on the take from the cartels by supporting them. Once Mexico is gone, the cartels will succumb. Then we can make Mexico into a US State. Think of the border freedom!

At this point, it seems more likely that the US government is taken over by the gangs, with the help of the weapons industry and the American Rifle Association.