As a mathematical concept, we can add or subtract anything. In chess, I can put point values on every piece, and keep score. At the end of the day, though, it's about checkmate. (Or stalemate, or time running out, if you play with a clock). A bishop is "worth" three points. So is a knight. A rook is "worth" five. If I trade a rook for a bishop, losing two points, and consequently checkmate you, you still lose.
But of course, trade isn't zero-sum, which is exactly where Trump goes wrong, as anyone who has studied economics in the last two centuries already knows. So, what's with this score thing?
We calculate "gross domestic product" by adding consumer spending, investment, government spending and net exports. If we have a trade deficit, that gets calculated into GDP as a reduction. OK, so is that bad? It lowers the number. Why is that the number that matters? Um...
We actually look at a lot of numbers to measure the economy. Unemployment, inflation, disposable income... What does the trade deficit have to do with that stuff? Less. Some, but less. That's not my real point today, though.
The flip side of a trade deficit, though, is a goods deficit for other countries. We're getting their stuff, and they're getting promissory notes that are worth, um... some imaginary thing. This is kind of like the arbitrary negative sign we assign to an electron. Why is that the negative charge? (Long story).
So, um, we trade with other countries in a way that means we get more of their stuff. Personally, I like stuff. I am typing this stuff on "stuff" right now, and it wasn't made in the US. Right now, the US is running a stuff surplus. That's the flip side of a trade deficit. They are mathematically equivalent.
Now, there's some bullshit here (more than "some"), and I may go into more on this because there are economic consequences to trade deficits. They are just minor, and Trump doesn't understand them. However, Trump only cares about keeping score and winning. Put this way, Trump would think we are winning.
And he wouldn't start this stupid, fucking trade war.