Donald Trump's famously nonspecific plan to make Mexico pay for a new, beautiful wall on the border between our two nations got slightly more specific on Tuesday. The campaign produced a memo for The Post specifying that Trump's plan was essentially to twist Mexico's arm behind its back -- threatening to stop wire transfers from noncitizens to places outside the United States. Or, to use the term with which the process is usually described, to try to block remittances from people working in the United States back to Mexico.

There are valid legal questions about whether Trump would actually have the power to do that as president, questions that The Post explored this morning. (Short answer: Probably not.) But given the regularity with which the topic has come up during Trump's candidacy, we figured we'd look a little more closely at the numbers behind remittances.

Mexico takes in about $2 billion a month in remittances.

The Bank of Mexico tracks how much the country receives in remittances on a monthly basis. In 2015, Mexico took in nearly $25 billion in total, including from countries besides the United States. But most of it was from the United States. (According to Pew Research, 98 percent of the remittances received in 2012 were from the U.S.)

January and February saw the smallest amounts come in.

Most remittances these days come into the country by electronic transfer.

In 1995, the first year for which data is available, about half of the remittances sent to Mexico came in the form of personal checks, money orders or cash. In February 2016, 98 percent of the money sent to Mexico from workers overseas was sent electronically -- the form that Trump is threatening to blockade.

Tracking remittances over time, you can see the same seasonality we noted in the 2015 data above. You can also see the sharp drop-off as the American economy tanked at the end of 2008.

The states that send the most money to Mexico are the biggest states.

This isn't rocket science, but it may defy expectations about the workers who are sending money back to Mexico. The state that sends the most is California, followed by Texas. But Illinois, Florida and New York also send a lot of money to Mexico (here shown on a quarterly basis).

What isn't known is how much of this money is being sent to Mexico from immigrants who are here illegally. Trump's memo to The Post asserts that Mexico receives "approximately $24 billion a year in remittances from Mexican nationals working in the United States" and that "the majority of that amount comes from illegal aliens." It's hard to evaluate that claim, but Pew's 2013 report suggests that it's likely to be true. "Some research has found that foreign-born U.S. citizens and legal permanent residents are less likely to send remittances than unauthorized immigrants who may have less attachment to the U.S. and more to their home country," Pew's researchers wrote.

Pew also noted in 2013 that remittances to Mexico were equivalent to 2 percent of the country's GDP. "Remittances," they wrote, "are a larger source of money to Latin America than official foreign aid."

Which appears to be why Trump thinks it's such a strong point of leverage.

What Donald Trump is doing on the campaign trail

U.S. Republican presidential nominee Donald Trump speaks at a campaign event at Trump Doral golf course in Miami, Florida, U.S. July 27, 2016. REUTERS/Carlo Allegri (Carlo Allegri/Reuters)