Reports that President Donald Trump wants to send 5,000 more troops to the Southern border, at first, come as a shock. It’s a startlingly high number. To put it in perspective, NATO recently deployed 4,500 troops in the Baltic nations to deter and repel a Russian tank assault. How many troops could possibly be needed to stave off an unarmed caravan of refugees walking up through Mexico—even if, as Trump and Vice President Mike Pence maintain, with no evidence, “Middle Eastern” terrorists are hiding in their midst?

As might be imagined, this is not a Pentagon initiative. Last week, Secretary of Defense James Mattis ordered a mere extra 800 troops to the border, to augment the 2,000 National Guard personnel sent there last spring, and even that seemed a bit of a sop to Trump’s clamoring.

News of a 5,000-troop upgrade, reported in Monday’s Wall Street Journal, may reflect a White House wishful dream. “Planning is still underway,” a Defense Department spokesman said Monday. “It remains premature to speculate total numbers or specific forces to be selected to accomplish the requested missions.”

One Pentagon official further told me that those “requested missions” came from the Department of Homeland Security as a list of desired capabilities. “It is the role of DOD planners to determine numbers” required for those capabilities, he said.

The Pentagon teems with creative bookkeepers, adept at stretching the “requirements” to whatever contours the commander desires.

These capabilities are not the stuff of combat brigades. In a Monday morning tweet about the caravan, Trump warned, “This is an invasion of our Country and our Military is waiting for you!” But the troops—however many they amount to—won’t be waiting with machine guns and artillery rockets. Rather, according to a Pentagon statement based on the DHS request, they will be providing support to the 16,000-plus Customs and Border Protection forces. “Support” is defined as engineers (for temporary barriers, barricades, and fencing), helicopters and planes (to move CBP personnel around), medical teams, command and control, temporary housing, and personal protective equipment.

When it comes to providing this sort of operational support, the Pentagon teems with highly creative bookkeepers, adept at stretching the “requirements” to whatever heights and lengths the commander desires. Recall last summer when Trump was pushing the Pentagon for a military parade in downtown Washington? Neither Mattis nor the officer corps really wanted to waste their time or money on empty showboating, so, all of a sudden, the estimated cost of the parade swelled from $12 million to $92 million—too expensive even for Trump, who canceled it. Similarly, if Trump wants to send 800 or 5,000 or 10,000 or however many troops to the Southwestern border, the Pentagon planners will devise a plan that fits the number.

Still, as a retired Army commander told me in an email Monday, “5,000 is a lot,” the size of “a very heavily augmented brigade combat team… Doable, but will require a lot of resources.”

Then again, Trump probably doesn’t care how many troops are sent, just as he doesn’t seem to care whether a “big beautiful wall” ever gets built. In his world, saying that something is true matters more than whether it really is true. Still, one wonders how much Mattis grinds his teeth at night. Neither he nor the brass could be happy about providing props and scenery for Trump’s Halloween election pageant, in which he drums up scary stories about dark-skinned goblins invading our fair land for the sake of boosting the Republican Party’s prospects in the midterms.