The issue here is more cultural than political, you know? In this country, the impunity rates are very high, because there's little to no social awareness and a large mass of corruption. That's one of the reasons I'm getting (pardon the expression) the hell outta there.
I've settled on Montreal for the time being, and I don't plan to come back any time soon.
Yes, violence has been present for a while now, but I don't think USA should be that worried. Whereas there's a lot of immigration, and the violence sites are close to USA, the government on USA is so different that it doesn't fit the position to allow such big things to go through.
You have to consider, though, that if Mexicans are spilling over the border is because USA neglected that on purpose at first (for cheap working force, among other reasons).
I do think the repercussions of what happens in Mexico will have influence on America (as a continent), since it is, after all, kind of a big country.
I don't like politics at all, you see. They make me sad.