Hey, didn’t Donald John Trump vow, declare it a lead-pipe cinch that Mexico would pay for a “big, beautiful wall” along the border between that country and the United States of America?

Didn’t he say he would force Mexico to foot the bill because, after all, those criminals and terrorists were “flooding” the country through our southern neighbor?

He got into an immediate war of words with Mexican President Enrique Pena Nieto after taking office this past January. Why? Pena Nieto said “no way” would his country spend a nickel to pay for the wall.

Here we are, nearly 100 days into the Trump administration’s existence. The wall is now central to a domestic political dispute — in the United States. The federal government might shut down if Congress cannot come up with a plan to stick American taxpayers with the bill to build a wall that (a) won’t work and (b) will blow up the annual budget deficit.

What’s the cost of this boondoggle? $20 billion to $25 billion? For starters?

Congress and the president are squabbling over whether to approve one of those “continuing resolutions” that would fund the government for the short term. Meanwhile, that damn wall is still being negotiated between Republican congressional leaders and the Republican who now sits (once in a while) in the Oval Office.

If there is a more impractical, illogical and ill-conceived idea than building such a barrier between two ostensibly “friendly” nations, then someone will have tell me.

A huge portion of the U.S.-Mexico border happens to be along a mighty river — the Rio Grande — that separates Texas from Mexico. How in the name of civil engineering does the president build the wall along that border? How does the president propose to seize all that private land without adding to the already-enormous cost? The U.S. Constitution’s Fifth Amendment requires “just compensation” for any “private land taken for public use.”

Well, why quibble over the small stuff?

The very notion of this wall becoming central to this political dispute simply illustrates yet another blind and thoughtless campaign promise the president cannot keep.

And if he made that promise knowing that he couldn’t fulfill it, isn’t that just another flat-out, bald-faced lie?