I am not a lawyer.

The role doesn't have that de facto power, but he could enact things that effectively make it the de jure law by forbidding US companies doing business with the US federal government from using anything that sources some or all of its goods and services that have a dependency on a Chinese supply chain. The anti-BDS rules that some states have is what I would consider to be the precedent here [0].

Given that the president also has frequent campaign rallies, he can persuade voters to boycott companies that again source components from a Chinese supply chain. His official campaign baseball caps aren't made in China though some unofficial ones are sold on Amazon that come from China [1]. I guess the same would go for US flags.

[0] https://en.wikipedia.org/wiki/Boycott,_Divestment_and_Sancti...

[1] https://www.snopes.com/fact-check/donald-trump-hat-china/

No he doesn't. It would require the law to change and he doesn't have that power. However he keeps increasing tariffs far enough I guess it's the same thing.

Not by tweeting, but I'm sure the US Government could through legislation implement something along the lines of "If you have any operations in america and the majority of your manufacturing/imports/etc. is in China, you have to move your manufacturing processes in x timeframe or subject to penalties."

Heard an opinion that he used that phrasing in order for it to get translated into Chinese a certain way.