Blocking remittances is probably impossible. Even if you could shut down all the direct channels for money to flow from US nationals to Mexican nationals, whic

Blocking remittances is probably impossible. Even if you could shut down all the direct channels for money to flow from US nationals to Mexican nationals, which you can't, it's trivial to either send easily resellable goods like gift cards or to transmit the money to some third party in a neutral country who agrees to forward it on for a small fee. Even if it were possible, blocking remittances is probably illegal under our free trade agreements with Mexico. Any attempt short of pulling out of NAFTA is all but guaranteed to be tied up in courts for years before it could possibly go into effect. And even if it were legal, a huge disruption to trade is all but guaranteed to cost the economy vastly more than the cost of just doing it ourselves (even assuming we actually wanted to). All of which is before you even consider the internal politics of getting the US congress to pass a bill in the first place, or of convincing the Mexican government to roll over and accept a huge insult without requiring anything in return. There is essentially no realistic model under which "it could certainly work". It's a feel-good idea that falls apart with the smallest amount of critical analysis. It's a childish conception of international relations, and any attempt to actually implement it is all but guaranteed to both fail miserably and make absolutely everybody worse off in the process.