Trump's been talking about tariffs for far longer than the current t-note cycle. He was talking about it a decade ago during his first time in office. IIRC he ran for POTUS as a Reform Party candidate in the 90s or 00s, and that party was started by Ross Perot, who was against NAFTA on the grounds that it'd cause a giant sucking sound of American jobs to Mexico.
He doesn't care about the debt; you can see this in how he pays taxes.
What he needs is something that lets the rich have their cake and eat it too. He needs to appear to be doing something for working-class American manufacturing jobs, while making the people that would fill those jobs bear the brunt of the impact. Tariffs are an expedient way to do that. They don't have to be approved by Congress and are effectively an autocratic way of raising taxes. They apply to prices first, not revenues, and they're simple to implement. The surplus value that used to head to shareholders as a result of cheap foreign goods will go down, but that can be offset by layoffs and the like.
The refinancing, if it's even a viable plan, is a nice side-effect.