You'd think iraq, afghanistan, both are so recent in history that he'd learn the lesson.
If you start trashing a country, pissing tons of people off big time, or exterminating some group of scumbags, be it the taliban, or saddam (not that in that case there was just cause for war, Saddam was a major-league dick, to be sure, but the WMD excuse, if they had anything, it might have been a forgotton sarin or mustard shell loaded into a rusted, useless wreck of an old ass howitzer, or something like that, loaded and left unfired, while the iraqi army fucked off, etc.. No stash ever found, and never will be either)
You leave a conflict like that un-finished, and look what happens, a power vacuum gets created. And what happens when you have a power vacuum? some group fills it. There might not be many nastier than ISIS but there are plenty of nasty packs of fundamentalist arseholes in the middle east. Leave the place a smoking wreck and don't bother finishing the job and tidying it up, people there, citizens, I mean, are going to hate your guts, and be ready for a scrap the next time the US interferes in syria. PISSED, because their homes were destroyed, families killed, etc. thats going to piss any nation off, big time.
And now the ISIS forces have more or less been given a good kicking, who is going to end up in their place. At least in afghanistan we tried to ensure there was a government. Syria is just a smoking crater, where chances are kids are going to be accidentally setting off unexploded ordnance for a long time to come and ending up as meatpaste. Government? WHAT government?
And assuming we haven't got each and every ISIS tosser, one left, means one still alive to espouse the same shit and try and get them going again.
Trump is a fucking moron, if you start a job, finish it. Or do not start it in the first place.
Of course in this case, not starting wasn't an option, ISIS had to go, because they were a murderous, raping, slave-dealing ancient archaeological site-defiling islamic sack of shit, and they needed to be burnt out of their hidey-holes, but to just walk off after the job is 3/4 done, thats asking for it.
Trump is one stupid bastard.