An explainer on the practicalities of a U.S.-Mexico border wall ?SECURE THE BORDER! BUILD A WALL!?
Like many of President Donald J. Trump?s policy pronouncements, his key campaign promise, the Mexican border wall, entered the world via an all-caps tweet on August 5, 2014. And like his initial long-shot bid for the White House, it now appears that this symbol of Trump?s America-first foreign policy platform is grinding toward reality.
Momentum for the wall began as soon as Trump appeared on Fox & Friends in January 2015 and ramped up throughout the primaries (competing candidates tried to outdo each other over how quickly they?d enact such a massive construction project). ?Build that wall!? became a unifying chant during Trump rallies leading up to the general election on November 8. And this January, this ?big, beautiful wall,? as our real estate mogul-turned-president fondly calls it, took the first step toward becoming U.S. government policy, as the president signed an executive order calling for the creation of ?a contiguous, physical wall or other similarly secure, contiguous, and impassable physical barrier.?
The Department of Homeland Security is set to announce, ?on or after March 8, 2017,? a formal request for proposals for the barrier?s design and construction.

Guillermo Arias/AFP/Getty Images
A view of the U.S.-Mexico border line in Nogales, northwestern Mexico.

If previous wall-building adventures are any guide, Trump may w...