Trump admits he punked his supporters on Mexico paying for the wall.

The Post's Greg Miller has obtained transcripts of President Trump's calls with the heads of Mexico and Australia during his first days in office, and they are both doozies.

One big takeaway is that Trump seems to acknowledge exactly what his pledge to make Mexico pay for the border wall was — a hollow promise meant to rile up the base.

At one point in his call with Mexican President Enrique Peña Nieto, Trump even acknowledges that the wall is “the least important thing we are talking about, but politically this might be the most important.”

You hear that, Trump supporters? That applause line that Trump used with such gusto for basically his entire campaign — “Build that wall,” and “Who's going to pay for it? (Crowd response: MEXICO!)"? It was all vote-bait, red meat for voters who didn't know that it was completely impractical and would never happen. And within his first days in office — this call took place on Jan. 27, a week after Trump's inauguration — Trump was already throwing in the towel on it on a call with the Mexican president.

Trump was instead hoping people could be made to forget this “least important” issue and wouldn't punish him politically for it.

Trump spent much of his call with Pena Nieto just trying to convince him to stop talking about how Mexico would not pay for the wall. Trump even suggested he would fudge it in the end so that both sides could claim they didn't give in.

“We should both say, ‘We will work it out.’ It will work out in the formula somehow,” Trump said. “As opposed to you saying, ‘We will not pay,’ and me saying, ‘We will not pay.’ ”

Pena Nieto said Trump's promise had put a “very big mark on our back” and “is an issue related to the dignity of Mexico and goes to the national pride of my country.” Trump's response to all of that was basically: Okay, well let's just stop talking about it publicly.

“But you cannot say that to the press,” Trump said. “The press is going to go with that, and I cannot live with that.”

Trump's promise to make Mexico pay for the wall stands out as perhaps both his biggest applause line and his most implausible policy idea on the 2016 campaign trail. The idea that Mexico would fund a wall built to prevent its own people from illegally crossing into the United States can't help but rub the Mexican people and Pena Nieto the wrong way. And it made Pena Nieto's appearance with Trump during the 2016 campaign a big political liability back home.

That meeting provided the first indication that Trump's border-wall promises would be problematic as president. Trump and Pena Nieto's office engaged in a public war of words over whether the wall was even discussed at their meeting.

It's little surprise to keen political observers that Mexico paying for the border wall was never actually going to happen. Hearing Trump basically acknowledge that fact and concede he pulled the wool over his supporters' eyes, just seven days into his presidency, is pretty remarkable.

Trump's supporters insist he's kept his promises thus far. Here's a good example of what he really thinks of one of his biggest promises.