Part of a fence that runs along the US-Mexico border. Reuters/Mike Blake

Building an impenetrable wall along the US-Mexican border, ostensibly to keep out foreigners, is a key item on President Donald Trump's campaign-promise checklist.

"I will build a great, great wall on our southern border, and I will have Mexico pay for that wall. Mark my words," Trump said during a campaign rally on June 16, 2015.

The president moved toward fulfilling that promise on Wednesday, January 25, 2017, when he signed a new executive order aimed at doing just that.

The order tasks the secretary of the Department of Homeland Security, a role currently filled by John Kelly, to "immediately plan, design, and construct a physical wall along the southern border, using appropriate materials and technology to most effectively achieve complete operational control[.]"

If Secretary Kelly is seeking technological inspiration for the design of Trump's wall, however, we hope he doesn't go rifling through the FBI's recently released dossier on Nikola Tesla, a prolific Serbian-American inventor — an investigation that, in a remarkable but purely coincidental twist, has a direct connection to the Trump family.

Tesla is famous for coming up with alternating current, which remains the world standard for delivering electricity. He also devised the induction motor, electrical bolt-shooting Tesla coil, and long-distance radio transmission (though he had his thunder stolen by a rival).

But Tesla also spun his deep understanding and explorations of electricity and radiation to dream up more nefarious inventions, including a "death ray" he described to Time Magazine in 1934, yet kept relatively quiet about.

Artists perform a show in Moscow using Tesla coils and protective suits. Pavel L Photo and Video/Shutterstock

The government did not forget this and was "vitally interested" in Tesla's unpublished research during a time of war and Soviet espionage. So after Tesla died in the New Yorker Hotel the evening of January 7, 1943, "his papers [...] were temporarily seized by the Department of Justice Alien Property Custodian Office ('alien' in this case means 'foreigner,' although Tesla was a US citizen)," according to the FBI.

Investigators and specialists examined the documents, recorded them on microfilm, wrote up reports, and added the material to their existing dossier on Tesla. The FBI waited decades to declassify the papers, releasing 250 pages of them as early as 2011.

But last September, the Bureau uploaded 64 new pages to its public file vault on Tesla, which we first heard about from Reddit user Pressrewind10.

Page 62, in a report titled "NY 65-12290", is particularly eyebrow-raising:

"TESLA's only military invention was a method to which he once eluded but nevr [sic] fully described. This invention was a means whereby an impenetrable [sic] 'wall of force' can be erected around the United States' borders which would render helpless any military attack. TESLA disclosed the existence of his plan in 1934 and stated he intended to present it to the Geneva Conference but seldom referred to it afterward."

A portrait of famed inventor Nikola Tesla at age 34. Wikimedia Commons (public domain)

Not much is publicly known about Tesla's impenetrable wall research beyond this. The only other details are presumably the ones he shared with New York Times writer William A. Lawrence, which the newspaper published on September 22, 1940:

"[Tesla] stands ready to divulge to the United States government the secret of his 'teleforce,' of which he said, 'airplane motors would be melted at a distance of 250 miles, so that an invisible "Chinese Wall of Defense" would be built around the country against any enemy attack by an enemy air force, no matter how large.'

"This 'teleforce' is based on an entirely new principle of physics, that 'no one has ever dreamed about,' different from the principles embodied in the in his inventions relating to the transmission of electrical power from a distance, for which he has received a number of basic patents."

Coincidentally after Tesla died, none other than electrical engineer and military technology researcher John G. Trump — President Trump's "nuclear" uncle, as an April 2016 New Yorker article by Amy Davidson dubbed him — was the person who examined Tesla's effects and reported his findings to the FBI.

Per Davidson, and according to Margaret Cheney and Robert Uth's book, "Tesla, Master of Lightning", John G. Trump told the Bureau:

"Tesla's 'thoughts and efforts during at least the past 15 years were primarily of a speculative, philosophical, and somewhat promotional character,' but 'did not include new, sound, workable principles or methods for realizing such results.'"

Congressional Republicans have said President Trump's wall will cost about $12 to $15 billion. However, analysts say a more realistic price tag, given what is known so far about the scope of the project, is likely to be about $25 billion.

We'll assume that slapping on some motor-melting teleforce fields would change that figure substantially.