There was a snippet on the news with a quote from President Obama. He was addressing Donald Trump's promise to build a border wall by taxing or threatening to end remittances from the U.S. to Mexico. It's an idea that has some merit. But Obama never misses an opportunity to criticize a political opponent. So he says this:
We just talked about the difficulties of trying to enforce huge outflows of capital. The notion we’re going to track every Western Union of money sent to Mexico—good luck with that.
So you need good luck to track money sent by Western Union to Mexico. Does anyone doubt that the Treasury, the FBI, or even the Federal Reserve isn't already tracking it? If they can get meta-data from the phone companies and bank transactions from banks, then remittances through Western Union seem like a piece of cake.
Only Obama would think his listeners wouldn't know that. Then again, maybe his listeners haven't been paying attention these past few years or don't actually have memories.