SO still no idea how to make Mexico pay for it, gotcha.

Introduction: The provision of the Patriot Act, Section 326 - the "know your customer" provision, compelling financial institutions to demand identity documents before opening accounts or conducting financial transactions is a fundamental element of the outline below. That section authorized the executive branch to issue detailed regulations on the subject, found at 31 CFR 130.120-121. It's an easy decision for Mexico: make a one-time payment of $5-10 billion to ensure that $24 billion continues to flow into their country year after year.

There are several ways to compel Mexico to pay for the wall including the following:

➤   On day 1 promulgate a "proposed rule" (regulation) amending 31 CFR 130.121 to redefine applicable financial institutions to include money transfer companies like Western Union, and redefine "account" to include wire transfers. Also include in the proposed rule a requirement that no alien may wire money outside of the United States unless the alien first provides a document establishing his lawful presence in the United States.

➤    On day 2 Mexico will immediately protest. They receive approximately $24 billion a year in remittances from Mexican nationals working in the United States. The majority of that amount comes from illegal aliens. It serves as de facto welfare for poor families in Mexico. There is no significant social safety net provided by the state in Mexico.

➤   On day 3 tell Mexico that if the Mexican government will contribute the funds needed to the United States to pay for the wall, the Trump Administration will not promulgate the final rule, and the regulation will not go into effect.

➤ Trade tariffs, or enforcement of existing trade rules: There is no doubt that Mexico is engaging in unfair subsidy behavior that has eliminated thousands of U.S. jobs, and which we are obligated to respond to; the impact of any tariffs on the price imports will be more than offset by the economic and income gains of increased production in the United States, in addition to revenue from any tariffs themselves. Mexico needs access to our markets much more than the reverse, so we have all the leverage and will win the negotiation. By definition, if you have a large trade deficit with a nation, it means they are selling far more to you than the reverse - thus they, not you, stand to lose from enforcing trade rules through tariffs (as has been done to save many U.S. industries in the past).
➤  Cancelling visas: Immigration is a privilege, not a right. Mexico is totally dependent on the United States as a release valve for its own poverty - our approvals of hundreds of thousands of visas to their nationals every year is one of our greatest leverage points. We also have leverage through business and tourist visas for important people in the Mexican economy. Keep in mind, the United States has already taken in 4X more migrants than any other country on planet earth, producing lower wages and higher unemployment for our own citizens and recent migrants.
➤  Visa fees: Even a small increase in visa fees would pay for the wall. This includes fees on border crossing cards, of which more than 1 million are issued a year. The border-crossing card is also one of the greatest sources of illegal immigration into the United States, via overstays. Mexico is also the single largest recipient of U.S. green cards, which confer a path to U.S. citizenship. Again, we have the leverage so Mexico will back down.