What did Donald Trump do today?

He either lied about the existence of his "wall," or something much worse happened.

Trump met today for what was supposed to be a private meeting and photo opportunity with incoming Speaker of the House designate Nancy Pelosi (D-CA), and Senate Majority Leader Chuck Schumer (D-NY). It quickly turned into a debacle for Trump, who addressed the press and immediately found himself boxed into a corner and vowing that he would be "proud to shut down the government" if he didn't get his way on funding for his border wall.

TRUMP: You know what I'll say? Yes. If we don't get what we want one way or the other, whether it's through you, through a military, through anything you want to call, I will shut down the government, absolutely. 

SCHUMER: Okay, fair enough. We disagree. We disagree. 

TRUMP: And I'll tell you what, I am proud to shut down the government for border security, Chuck, because the people of this country don't want criminals and people that have lots of problems, and drugs pouring into our country. 

So I will take the mantle. I will be the to shut it down. I'm not going to blame you for it. The last time you shut it down it didn't work. I will take the mantle of shutting down, and I'm going to shut it down for border security. 

SCHUMER: But we believe you shouldn't shut it down.

Trump, whose mood had visibly soured by this point, then had the press herded out.

But Trump has a long and bizarre history of demanding shutdowns, in spite of the extraordinary expense and inconvenience they cause Americans, so this is not exactly news. Of more immediate interest from his remarks today is Trump's apparent belief that the border wall he has been talking about since 2015 has actually been built:

One thing that I do have to say is tremendous amounts of wall have already been built, and a lot of wall when you include the renovation of existing fences and walls renovated a tremendous amount, and we’ve done a lot of work. In San Diego we’re building new walls right now. And we’ve — right next to San Diego, we’ve completed a major section of wall, and it’s really worked well. So a lot of wall has been built. We don’t talk about that, but we might as well start because it’s being built right now. Big sections of wall. And we will continue that. And one way or the other it’s going to get built.

In simplest terms, none of this is true.

All construction on border fencing undertaken since Trump took office has been a continuation of routine repair, most recently authorized under the Secure Fence Act of 2006. Not a single inch of Trump's imagined wall has been built. But Trump has repeated the lie so many times that this week it became one of a brand new class of lies tracked by the Washington Post: the "bottomless Pinocchio" for flagrant lies that Trump insists on repeating no matter how often they are debunked. (By the Post's count, Trump has claimed or imagined the existence of his wall 86 times as of today.)

At no point during Trump's threats to shut down the United States government over "the wall" did he acknowledge his long-since abandoned promise that Mexican taxpayers would pay for it.

Who cares?

• Voters who heard Trump insist hundreds of times that he would make Mexico pay for the wall may have thought he was going to make Mexico pay for the wall.

• It's extremely bad if a president genuinely doesn't know that his centerpiece domestic policy hasn't actually been implemented.

• The functioning of the American government is more important than a president's political needs.