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I don't quite see what OP's point is. If it is finding an use for the US contingent, getting rid of more or less deprecated equipment and overall just getting something to throw public money at, yes, it is a rather good idea. >>13960's approach seems the most reasonable on those topics.
A parallel internal operation would be necessary aswell. Reinforcing the border can only do so much, the cartels are at least operating business in the US soil already and terrorism is cheap as ever.
But that's mostly to show some work and rather clumsily isolate the US from the situation.
Now, an intervention intending to really bring peace into Mexico wouldn't be mostly militar at all. First there'd be much work to do on cleaning corruption from Mexico's military/government, cutting bank accounts(then punishing the responsible for covering them, which is as impracticable as legalizing drugs) and whatnot before any military operation becomes viable.
Then, organizing such intervention would be complicated. Mexico's policial and military forces seem to be completely demoralized or just completely dissolved in some areas, a joint force would be definitely necessary, if only to provide numbers.
On dismantling the cartels themselves I have no idea, big numbers and superior equipment can't really do much agains't modern guerrillas.
At least restoring safety to the civilians and preventing attacks on infrastructure, in short, giving conditions to the state regenerate itself, is crucial. But easier said than done, and any further dissertation would require knowledge in what networks are there to be disrupted, how would one do that and its effects, which I don't have.
All that while working on the border and internally to avoid retaliation on US soil, which is a lot easier than it is for middle eastern groups.
So, tl;dr reinforcing Mexico's military, focus on preventing state failure and hoping for breakthroughs on how to deal with such groups(which I don't believe the US has perfected enough), but only after a thorough cleanup.