After "Make America Great Again," it is perhaps the most common refrain of the Donald Trump campaign.

"I will build a wall!"

And, every time, it's followed by an ironclad guarantee from the candidate:

"And I will make Mexico pay for it."

When asked how, Trump has always been short on details. He cites leverage the U.S. has over Mexico, which needs access to the U.S. market. He has also suggested steep tariffs on Mexican-made goods.

But now comes a bit more detail — in a memo just over a page long — first reported by the Washington Post and now posted on the official Trump campaign website.

It's still all about leverage.

The memo lays out a three-day plan, using provisions of the Patriot Act, that Trump says will "compel Mexico to pay for the wall."

The basic argument is this: Billions of dollars in cash are transferred by individuals from the U.S. to Mexico every year. To keep that from coming to a halt, Mexico must make a one-time payment to the United States of $5 billion to $10 billion. That amount would cover the cost of building a wall that Trump has estimated would carry a price tag of about $8 billion. (Incidentally, that figure that is widely criticized as being far too low.)

Day 1: The Trump administration would draw up a "proposed rule" stating that no one be allowed to wire money outside the U.S. "unless the alien first provides a document establishing his lawful presence in the United States."

Day 2: Here the memo predicts that "Mexico will immediately protest." It goes on: "They receive approximately $24 billion a year in remittances from Mexican nationals working in the United States." A 2013 Pew Research study, based on World Bank data, put remittances from the U.S. to Mexico at nearly $23 billion, so that's close to the amount Trump's memo cites, but the campaign offers no evidence to support a claim that "The majority of that amount comes from illegal aliens." (Remittances to Mexico were up almost 14 percent in February, NPR's Carrie Kahn reports from Mexico City, per BBVA Research.)

Day 3: Tell Mexico that if it agrees to come up with the cash to pay for the wall, then the "proposed rule" will never go into effect.

Further, Trump says the U.S. can use tariffs and strict enforcement of existing trade rules. The memo maintains that any price increases Americans see as a result of such policies would be "more than offset by the economic and income gains of increased production in the United States." In addition to that, there would be the cancellation of visas for Mexican citizens coming into the U.S., including business and tourist visas.

In short, pay up or risk an all-out trade war with the U.S., writing new punitive measures that Trump says Mexico couldn't bear.

President Obama dismissed Trump's plan as politics and "half-baked." He called his plan to halt remittances "impractical" and said that the U.S. wasn't going to track every Western Union package.

"We've got serious problems here," Obama said from the White House Briefing Room. "We've got big issues around the world."

(Obama also tried to widen the lens not just on Trump but to the rest of the GOP, hitting "concerns" about Ted Cruz's proposals as well.)

Mexico is an ally, which the memo asserts in its conclusion "has taken advantage of us in another way as well: gangs, drug traffickers and cartels have freely exploited our open borders and committed vast numbers of crimes inside the United States. The United States has borne the extraordinary daily cost of this criminal activity."

It closes by saying the U.S. has the moral high ground, and it's time "we use it to Make America Great Again."

So far, there's been no official reaction from the Mexican government to all of this, but in the past there have been strong statements in opposition to Trump's calls for the country to pay for a wall.

Last month, President Enrique Pena Nieto told the Excelsior newspaper that there is no scenario under which Mexico would do that. At the time, he also stressed the importance of the long-standing alliance and friendship between the two nations and said Mexico will work with the next U.S. president to continue that.

That followed even stronger language from former Mexican President Vicente Fox in an interview with U.S.-based Univision. Fox responded with a vulgar exclamation when asked about Trump's demand, stressing Mexico will not "pay for that [expletive] wall."

He went on to call Trump a "crazy guy," adding that the billionaire candidate "should pay for it. He's got the money."

That was back in February, and, at the time, Trump responded during a GOP debate on CNN, saying, "The wall just got 10 feet taller, believe me. It just got 10 feet taller."

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