When Donald Trump decided last week that he would circumvent Congress and build a border barrier through an emergency declaration, it created a tricky budgetary challenge. After all, it’s not as if the Treasury can just cut the president a check for $8 billion. The money would have to come from somewhere.

And so, administration officials identified some pots of money from which to divert funds. As of last week, the Washington Post reported that the plan involved taking $600 million from the Treasury Department’s forfeiture funds account, $3.6 billion from military construction, and $2.5 billion from a Pentagon program for countering drug activities.

Of course, the list of hurdles between the White House crafting and executing such a plan is significant. Will Congress block the president’s gambit? Will the courts tolerate the power-grab?

Before those questions can be answered, Roll Call reports on an expected problem: the money Team Trump thought would be available might not entirely exist.

More than one-third of the money President Donald Trump wants to redirect from other federal programs to build a border barrier is likely to be unavailable from the sources he has identified. As a result, it may be difficult for the president to circumvent Congress, even if a resolution disapproving of his “emergency” moves is never enacted.

The aforementioned Pentagon program for countering drug activities apparently has $85 million in unspent funds. Trump intended to take $2.5 billion from it.

Oops.

At this point, it’s not altogether clear whether there was some kind of mistake that led officials to believe there was more money available than actually existed. Whatever happened, if the Roll Call reporting is correct, Trump’s $8 billion plan is suddenly $2 billion short.

So what happens now? The article added, “The Pentagon is planning to ask Congress for authority to reprogram more than $2.4 billion from other military programs into the counterdrug account in order to then take it right back out and move it to the wall project…. A reprogramming request must be approved by both Republicans and Democrats on the four authorizing and appropriating panels that oversee the Pentagon.”

House Democrats may have some thoughts on the matter. Call it a hunch.

In the meantime, House Democratic leaders announced this morning that members will vote on Tuesday on a bill to block the president’s emergency declaration. It will need a simple majority to advance – which shouldn’t be a problem in the Democratic-led chamber – before heading to the Senate.

In this case, the Republican majority in the upper chamber will have to act on the measure, whether Mitch McConnell (R-Ky.) likes it or not.

We’ll have much more on the legislation on Monday.

Postscript: The measure to block Trump’s scheme already has 222 co-sponsors in the House. Since it needs 218 votes to pass, I like its chances.