I refer to the west coast states as "Pacifica," whether or not we secede. The question is: let's fire up those 30% tariffs. Let's also assume that Canada and Mexico don't take it lying down, and impose similar retaliatory tariffs. Trade across our two borders trickles to nothing.
Now, Pacifica says, "We'll honor the Free Trade Agreement that Trump violated" and takes over the borders with Canada and Mexico. Goods can be imported into Washington and California without tariffs. Pacifica will reap the benefits of free trade, while Trumpland crumbles as they discover how dependent they were on imprted goods as well as export markets.
Now, of course, the orange bully would demand that Pacifica cede trade regulation authority back to the federal government. But what if Pacifica refused? Would he send an army? I doubt that he has the balls. Like all bullies, he's at heart, a coward. (Also, no guarantee that army would win.)
Pacifica would be the richest nation on earth within a decade. Good riddance to Trumpland!