TRENTON — President Donald Trump’s called for “wall” along the southern border with Mexico would be a series of fences and barriers that would cost as much as $21.6 billion — almost double what he claimed it would — according to an a internal Homeland Security report seen by the Reuters news agency.

The report is expected to be presented to Department of Homeland Security (DHS) Secretary John Kelly in coming days, although the administration is not necessarily bound to take the actions it recommends.

The plan calls for securing the border with an additional 1,250 miles of fences and walls by the end of 2020.

Currently, 654 miles of the U.S. southern border are already fortified.

The report seen by Reuters is the work of a group commissioned by Kelly as a final step before moving forward with requesting U.S. taxpayer funds from Congress this spring and beginning construction in September.

On Wednesday, the president told a Washington D.C. meeting of law enforcement officials gathered from around the nation that “the wall is getting designed right now.”

The DHS report says construction would have three phases.

The first phase — and smallest —  covers 26 miles near San Diego, California; El Paso, Texas and in Texas’s Rio Grande Valley.

The second phase covers 151 miles in and around the Rio Grande Valley; Laredo, Texas; Tucson, Arizona; El Paso, Texas and Big Bend, Texas.

The third phase would cover the remaining 1,080 miles. However, much of that land is privately owned, inaccessible by road or is comprised of challenging terrain where it would may not be feasible to build a wall, like mountains or the middle of rivers.

Trump will first ask Congress, not Mexico, to pay for wall

Reuters quoted a source within DHS saying that the Trump administration would likely need to seize hundreds of miles of the privately-owned borderland from U.S. citizens under eminent domain in order to embark on the final phase.

The ensuing legal battle could add drive constructions cost up to as much as $25 billion, according to Bernstein Research, an investment research group that tracks material costs.

To put that in context, the entire annual budget for NASA is less than $20 billion.

Trump has insisted from the start of his campaign that Mexico would agree to pay for the wall.

Last month, Mexican president Pena Nieto canceled a planning meeting with Trump after Trump tweeted that unless the U.S.’s third largest trading partner agreed to pay for the wall, it was better not to meet at all.

Pena Nieto responded in his own tweet  that “Mexico offers and demands respect, as a the sovereign Nation that we are,” and added, “I’ve said it many times before — Mexico will not pay for this wall.” 

That’s something that Gov. Chris Christie had previously argued as well.

A month before embarking on his own presidential bid, the governor professed “I’m not a guy who’s been in favor of building a wall or a fence along the entire southern border…because it’s too expensive and too inefficient,” and adding that those who are “determined to get over, around or under” such structures invariably do.

A DHS spokeswoman said the department does “not comment on or confirm the potential existence of pre-decisional, deliberative documents.”

Claude Brodesser-Akner may be reached at cbrodesser@njadvancemedia.com. Follow him on Twitter @ClaudeBrodesser. Find NJ.com Politics on Facebook.

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