The difference is that Mexican drug dealers are not going to place explosives in hotels or city centers, they are not going to wage war against the US army, they will not pose a threat to the nation's sovereignity.Then on what basis you are badgering constantly that Pakistan army failed to pile up such weapon stash ? Borders are porous, Underground tunnels exist every where in border regions. But criticism comes cheap I guess
There is a lot of drug related violence, especially since the govt ill advisedly started the "war on drugs" thing, but it is not an insurgency - it is a matter of law and order only.
If Mexican drug dealers were coming into the US to wage war against the US, you can bet your last fix of meth, that the US govt would not only seal the borders, but would probably eviscerate Mexico.