I think you are the one that doesn't understand. It has been clearly stated by the White House that this is related to the trade deficit. They even stated that they rejected Vietnam's proposal to drop tariffs since it didn't address the trade deficit.
When he went off about that, the first thing I thought: "But, Mr. President, did you bother to call any of them before you enacted the tariffs?" Nothing but a clown. 💩
Much like how vaping has been bundled with smoking when it comes to rules/laws (vaping does not produce smoke), not all vaping involves potentially harmful chemicals. Vaping dry herb does not introduce any chemicals. One is just evaporating the naturally occurring contents of said herb.