Trump has made it crystal clear that he doesn’t believe the platitudes about how awesome the free market is. He believes all the worst things about the free market that a freshly-minted Marxist does, he just thinks they’re features instead of bugs. Trump doesn’t believe in the win-win, utility-maximizing transaction where the demand and supply curves cross, like the first day of Economics 101. He believes every transaction has a definite winner and a loser, it’s just that he thinks himself shrewd and ruthless enough to always be the winner.
It’s one of the sources of his success with the uneducated white lower class: they feel like they’re the definite loser of every transaction they’ve been in, and they think because Trump recognizes it that he’s on their side. It’s also why he has utter contempt for everyone he does business with. He doesn’t see their success and his as linked in any way (developer-contractor, employer-employee, etc.), he sees them as adversaries he’s already defeated.
Trump also doesn’t believe in free trade, where each nation follows its comparative advantage and makes what it makes best while other nations make what they make best and everyone’s better off. Which again is an abstraction, as a nation can collectively be better off from free trade and have sectors that aren’t better off, etc. To Trump, every nation that sells us something has just fucked us over. The more they sell the more they fuck us over. And it is "nations" to him: VW doesn’t sell cars to American individuals, Germany or the EU sells cars to the US. Nobody is a bigger believer in autarky than Trump, he’s more Juche than the Kims.
Except his overweening need to be the winner means he wants not an autarkic America but an economically conquering America that sells massive amounts of goods to the world while buying nothing from abroad. However improbable or unsustainable that is.
And that’s another source of his success with his base: people who remember, or were told by their parents, of the postwar years into the '50s when the US seemingly DID sell most everything to the rest of the world while buying little from abroad. It’s beyond their thinking that such a situation did not exist before the destruction of the war and could not exist too much longer after the war once nations started rebuilding their industry and infrastructure. They’ve convinced themselves, because these circumstances prevailed in their childhoods or early adulthoods, that this transient postwar anomaly was somehow the normal situation.
Sufficiently annoyed countries might stop using the USD as a reserve currency, or even investing in the US if they smell discrimination or think the US dismantling of consumer and investor protections means they no longer respect the rule of law.