What he wants is autarky.

Trump has always had this really skewed understanding of business and trade where he sees everything as a zero-sum game (whatever someone else gains, you must be losing). This, combined with his middle school understanding of economics, causes him to see trade deficits as fundamentally negative, as if they somehow represent money that the country is losing.

This just isn't how reality works. I could look at the balance of trade between me and my grocery store and it would be 100% negative, but I'm still getting food in return for the money I spend. The question is "Am I getting good value for money, and am I spending within my means?" Trade deficits haven't really mattered since we all moved off of precious metal backed currencies.

Trump doesn't get that, so he thinks it's somehow important for the US to at least run a surplus with all their trade partners, or better yet simply not trade at all and keep the entire economy 100% self contained.

Also, on a more personal level, he just wants trade wars because they make him feel good. He's a deeply insecure man and slapping tariffs on other countries feels big and muscular, like he's swinging punches but with money. That's why his tariffs are always blanket, never precisely targeted.

That's why NAFTA got renamed to the USMCA; a new name that put America first made Trump feel like he was getting a win.