The short address about Afghanistan on Monday evening was among the least offensive speeches Trump has delivered. Not because he stuck to the script, but because literally any proposed "solution" to that ongoing conflict is approximately as stupid as any other.
There is no solution. Obama knew it, and the people with half a brain around Trump know it too. The options are (to coopt language from an equally long and lamentable conflict) to "Vietnamize" the problem, to do nothing, to bring everybody home, and to send more people over. Clearly the practical solution is to just pull the plug and bring everyone home. But since we can never admit a mistake or resist the pull of the sunk costs fallacy, that's politically infeasible even for a president who isn't a monster.
Vietnamize it? Give me a break. The Afghan government barely exercises any sovereignty in the country's urban centers. Go five miles outside the security perimeter established by the American military and that country is lawless. They have zero capacity, even after 15 years of throwing money and (military oriented) solutions at the problem. So (presumably Mattis) decides, what the hell let's send 10,000 more people there, or whatever. It's a token gesture likely to accomplish nothing in the short term and less than nothing in the long term.
This is why we were so vocal about the dumbass logic used to support intervention in Iraq and Afghanistan – because once you become embroiled in this kind of situation, it is next to impossible to get out. You become, as the trillion dollar military ours is, the main institution of power in an otherwise weak, ineffectual, corrupt, and impotent government. And a few years in you realize that no amount of treasure and patience and pleading is going to get this puppet government to do the things you believe it should be able to do, so the options are reduced to pulling out and watching the whole thing collapse Saigon '75 style or you do what we are doing right now which is to make an essentially eternal commitment to fighting a low level insurgency in a country you don't fully comprehend and in which you are distinctly unwanted.
The only thing that makes any sense is cutting bait, and the conflict has been back-burnered so completely with the American public that there will never be a critical mass of public opposition to force Congress and the Pentagon to pursue that course. The DoD found the perfect heat setting to maintain the war on a low simmer, barely noticeable except for the people who are directly being shattered by it. Maybe that's the lesson they learned from Vietnam – abolish the draft and keep the troop levels low enough that eventually people will just kinda forget about it.
If that was the plan, it worked.