Sure I can. That $20 went to an American company to pay American salaries and provide an American profit. Those salaries and profit in turn get spent primarily in the American market.
But in your buy foriegn scenario, you spend $15 on a chinese made shirt. $0.50 of that went to a Chinese worker, and will recycle primarily in chinese economy and the Communist government took about $13, leaving $1.50 for profit. So of your $15, maybe 2.00 comes back to buy trade goods and $13 comes back to buy debt. Plus of course your $5 savings, but you spent that at Wal-mart for more Chinese made goods.
So in the first scenario we have the full $20 multiplying throughout the American economy putting people to work. In the second scenario, we've got only $2-$3 recycling through the American economy and the other $17 is coming back to buy our debt or more of our companies to dismantle.
In the first scenario, that $20 paid income taxes, and the rest got spent, generating more income taxes, and again, as the multiplier wound down. In the second scenario, your neighbor Todd had to file unemployment.
In the second scenario you saved $5.00, less the additional taxes you'll eventually have to pay to support your neighbor Todd, less the additional taxes you'll have to pay because Todd is no longer paying his fair share of taxes, plus the interest on the debt that the government had to borrow because Todd's not paying his fair share and the goverment has to support him, less the downstream effects.
It wasn't just Todd, but Sarah at the thread manufacturer and Jim at the Machine repair company that all lost their jobs when Todd lost his. And since Todd, Sarah and Jim aren't working, they aren't buying from you so your sales are down too. Maybe you can get the Chinese to buy from you before you join Todd in the unemployment line. Good luck with that.