President Donald Trump talks with reporters after reviewing border wall prototypes, Tuesday, March 13, 2018, in San Diego.
Evan Vucci/AP Photo

A wall would cost far more than $5 billion, so why have this fight?

As the government gets set to shut down in about 12 hours, there’s apparently only one number that matters: $5 billion. That’s the only line on Donald Trump’s ransom note to Congress. If lawmakers agree to turn over the $5 billion for his border-wall project, he’ll keep the government open. If they don’t, he’ll shut the government down – “for a very long time.”

But it’s worth pausing to ask an awkward question: how exactly did we arrive at this specific figure?

In February 2017, Reuters published an interesting report on the project’s price tag.

President Donald Trump’s “wall” along the U.S.-Mexico border would be a series of fences and walls that would cost as much as $21.6 billion, and take more than three years to construct, based on a U.S. Department of Homeland Security internal report seen by Reuters on Thursday.

The report’s estimated price-tag is much higher than a $12-billion figure cited by Trump in his campaign and estimates as high as $15 billion from Republican House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell.

Trump himself gave the project a $20 billion price tag, while a Politico  report, citing estimates from Capitol Hill sources, added that some lawmakers believe the price “could be as high as $50 billion when all is said and done.”

As Vox’s Matt Yglesias noted yesterday, the White House put together a budget request last year seeking $25 billion for the project.

So, putting aside related angles – I seem to recall Trump promising Mexico would pony up money for this – why is the fight over $5 billion?

As best as I can tell, Trump picked an arbitrary number that sounded good, knowing that it’d be tougher to get even House Republicans to go along with the $25 billion request the White House made a year ago.

Sure, $5 billion won’t build much of a wall, but during the president’s re-election bid, he’d be able to tell his followers, “Against all odds, I secured the funds needed to start the wall. Give me a second term, and I’ll finish the job.”

It won’t be a great argument – there’s still the whole Mexican-financing thing to consider – but Trump also knows that if he gets nothing, which now appears very likely, he’s going to have a tough time explaining to voters why he failed so spectacularly on his signature issue.

With this in mind, assuming there is a shutdown, I expect Trump to start lowering his target price, in the hopes that Democrats give him something to help him save face. I have a hunch this won’t work, but time will tell.