I see your point, but I think what he attempted to do was doomed to fail.
Trump thought he could bully Xi like he bullied Canada, Mexico, and the EU- that was indeed 'naive' and 'misinformed'- Xi didn't give an inch, and showed he was more than willing to play the long game. There were many among that 'army of strategists' that predicted exactly what has so far happened, that this would come to the point where it wasn't politically expedient for Trump, and he'd back off- Trump didn't listen to them. Look at the BS reason he gave for delaying the tariffs- it's a 'Christmas gift' for US consumers...

He's been saying for months that 'China is paying the tariffs' and that they're adding billions to the US coffers- wouldn't implementing the tariffs have been the 'Christmas gift'? He basically admitted who really pays the price (in the form of what is essentially a tax increase) after all.
As far as 'a more opportune time' goes, he should have waited until his second term (if he ends up getting one- he probably will, but this is something the Dem candidate is absolutely going to use against him, and likely with some effect)- he wouldn't have had to take the step back (based on worrying about losing support from his agricultural base) and had his position weakened, but he thought he was going to win the trade war easily and this would be a good thing to campaign upon- nope.
There never seemed to be a real 'end game'- it was all about trying to force China to the table in a weakened position where they'd agree to anything he wanted (he actually thought he could force the Chinese parliament to legislate laws that would be specifically favorable to the US)- so, why is he backing off? Inflicting damage has to have some purpose beyond a feeling of satisfaction or revenge when you're taking damage in return, otherwise it becomes the embodiment of 'cutting off your nose to spite your face.'
As always, I have a 'let's see what happens' attitude, but I think (since he started this tariff war, which I thought was a bad idea from the beginning, but if we're already in it) he should have held steadfast in his resolve to win it. Maybe he'll pick it back up again if he wins in 2020 (or perhaps he'll go ahead with the new tariffs in December as he said he would after delaying them from September 1st), but his actions this week will only have emboldened Xi to continue on the same course of tit-for-tat trading of blows rather than capitulating, imho- just waiting it out seems to be a viable strategy for him, especially with the current uncertainty in the markets, which makes a protracted trade war a much less palatable option for Trump.