Insiders close to the Trump White House say that as the President seeks to improve the U.S. position in NAFTA, a key talking point will be getting Mexico to build a border wall across its southern border.

The Trump administration, by improved enforcement, has already caused illegal border crossings from Mexico to fall dramatically, with some data showing drop-offs of up to 60 percent over last year.

But other data suggest that illegals crossing the U.S.-Mexico border are not Mexicans, but largely citizens of Guatemala, Honduras and El Salvador.

These illegals first cross Mexico’s southern border, transit across Mexico and then illegally cross into the U.S.

If Mexico would build a wall and beef up security across its own 732-mile border with Guatemala and Belize, the effect on illegal crossings into the U.S. could be dramatic.

The costs savings would also be huge – just a fraction of the estimated $21 billion a wall across the 1,989-mile U.S. border would cost.

New White House chief of staff John Kelly has been an advocate of focusing on the source of the illegals emanating from Guatemala, Honduras and El Salvador.

As Secretary of Homeland Security, Kelly had told the Senate: "Border security for the United States starts 1,500 miles to the south."

In 2017, Border Patrol apprehensions of families and children coming across the U.S. Mexican border show that only 4 percent are Mexican nationals, the remainder are from nations south of Mexico.

And a Pew Study two years ago showed that non-Mexicans crossing illegally outnumbered Mexicans.

The trend of illegals escaping Central American poverty and violence has continued despite Mexico’s efforts to control it. The trend includes the well over 100,000 unaccompanied minors who journeyed to the United States to flee gang violence and the drug cartels.

Mexico claims it has cracked down on the northern flow of migrants from Guatemala, Honduras, and El Salvador since the 2014 adoption of its comprehensive southern border plan,

In 2015, Mexican authorities reportedly arrested over 170,000 Central Americans trying to march north to reach the United States.

Still many continue to make the trek enduring the risk of robberies, beatings, and rapes.

And unlike the U.S.-Mexico border, which tends to have defensive fortifications and is heavily patrolled, Mexico’s southern border is relatively remote and porous.

According to one CNN report, anyone can purchase a boat ride across the muddy Suchiate River from Guatemala to Mexico for the princely sum of 25 pesos, or about $1.25. Fencing between the two countries, which is often used to control the movements of livestock rather than people, is rare.

There are only about a dozen official crossing stations on Mexico’s southern border — and over 370 commonly used unofficial crossing locations, according to the Guardian.

Earlier this year Stratfor, the respected geopolitical intelligence group, reported that the Trump administration “is considering helping Mexico increase security at its southern border with Guatemala.”

Stratfor’s analysts stated it would “likely be cheaper to implement than additions to the U.S.-Mexico border fence because of the comparatively shorter length of Mexico’s border with Guatemala, and because roads and rail lines into Southern Mexico would be easier to choke off than the ones at the much larger U.S.-Mexican border.”

Some conservatives have advocated for a push to secure Mexico’s southern border. Weekly Standard editor Ethan Epstein said earlier this year that helping Mexico gain control of its southern border is “a notion that makes a good deal of sense.”

In February, U.S. officials met with their Mexican counterparts near the Mexico-Guatemala border to discuss how the administration could help fortify it.

The substance of the discussions have yet to be made public.

Mexico’s southern border fortifications could emerge as a negotiating point in the NAFTA negotiations, sources say. Mexico itself would figure to benefit because it would finally be able to control the influx of undocumented immigrants across its own southern border.

According to published reports, Canada, the United States, and Mexico remain deadlocked on a range of NAFTA issues, with negotiations slated to resume in Ottawa from Sept. 23rd

And Mexico remains in adamant opposition to a U.S. border wall.

As recently as Aug. 27, Mexico’s ministry of foreign affairs stated: “Our country will not pay, under any circumstances, for a wall or physical barrier that is built on U.S. territory along the border with Mexico. This determination is not part of a Mexican negotiating strategy, but a principle of national sovereignty and dignity.”

But Mexico’s statement leaves open the door for a Mexican built wall on it southern border.