White House officials made the unusual decision Tuesday to allow cameras to film a nearly hour-long immigration meeting with a bipartisan group of lawmakers. They probably wish they hadn't.

For a moment, Democrats thought they had struck an unexpected deal with President Trump. Trump had previously insisted that any deal protecting "dreamers" — undocumented immigrants brought to the United States as children — should also include border security and/or a border wall. But he now says that he would support a “clean” bill protecting dreamers, and then take up comprehensive immigration reform later.

“What about a clean DACA bill now, with a commitment that we go into a comprehensive immigration reform procedure?” asked Sen. Dianne Feinstein (D-Calif.). Trump responded: “Yeah, I would like to do that. I think a lot of people would like to see that.”

The problem? Trump didn't know what “clean DACA bill” meant. House Majority Leader Kevin McCarthy (R-Calif.) quickly interjected and made clear that Trump believes a “clean” bill would include border security. Except that's not at all what a clean bill is; that's a compromise bill. A clean bill, by definition, only has one component to it.

By the end, Trump sought to clarify things. “I think a clean DACA bill to me is a DACA bill, but we take care of the 800,000 people,” he said. “But I think to me, a clean bill is a bill of DACA — we take care of them, and we also take care of security.”

If anything, the whole mess showed pretty vividly just how utterly disengaged Trump is in the finer details of policy discussions. Which is exactly the perception that he has recently fought against.

Asked by the New York Times late last month about this perception, Trump bristled. “I know the details of taxes better than anybody — better than the greatest CPA,” he said. “I know the details of health care better than most, better than most.”

The problem is that every public indication gives us the opposite impression. Trump almost continually moves the goal posts on what he wants, shifts the terms of the debate, and misstates what's actually contained in the legislation that is before Congress.

The Washington Post's Josh Dawsey said it well:

Even by the end of the meeting, Trump seemed to indicate that the border wall isn't necessarily a must-have for him — becoming just the latest iteration in a dizzying series of back-and-forths on what he wants in a DACA deal.

“I think my positions are going to be what the people in this room come up with,” Trump said. He added: “I'm not going to say, 'Oh, gee, I want this,' or 'I want that.' I will be signing it.”

Okay, so you're no longer demanding the border wall or even border security, then?

If you are a Democrat hearing those words, it's pretty clear that Trump isn't wedded to his position on, well, anything. The border wall seems more like an opening bid. If Trump has shown us anything, it's that he just wants to sign bills and make sure the base doesn't hate him for it. So as long as he can plausibly say he fought the good fight for the border wall — even if he didn't — it seems he's ready to just get it over with and claim a legislative win.

Which is generally okay! Presidents needn't dirty their hands with all of the sausage-making that happens down Pennsylvania Avenue. Congress produces the bills, and the president decides whether to sign them.

But Trump has repeatedly assured us that he knows this stuff better than almost anyone and that he's the world's preeminent negotiator. What we saw Tuesday was neither of those things.

Update: As The Post's Ashley Parker and Philip Rucker report, Trump's "Yeah, I would like to do that" line was conveniently left out of the White House's transcript:

THE PRESIDENT:  I remember that.  I have no problem.  I think that's basically what Dick is saying.  We're going to come up with DACA.  We're going to do DACA, and then we can start immediately on the phase two, which would be comprehensive.

SENATOR FEINSTEIN:  Would you be agreeable to that?

THE PRESIDENT:  I think a lot of people would like to see that, but I think we have to do DACA first.