Trump's cornerstone campaign promise has become a muddled mess. And even Republicans in Congress don't know what Trump wants anymore.

Nobody understands Donald Trump’s harebrained plan to build a wall along the border between the United States and Mexico, and that includes some Republican members of Congress.

Trump’s border wall was a signature promise of his xenophobic presidential campaign, as he promised it would be a 1,900-mile long wall to completely block off the border.

But now, like so many of his proposals, Trump’s policy has become completely muddled, part fiction and part law enforcement fantasy.

For starters, a clear majority of voters don’t want the government spending billions and billions of taxpayer dollars to build a wall. Secondly, it’s not feasible and it’s never been feasible.

On Tuesday, the White House staged a 55-minute photo-op featuring Republican and Democratic members of Congress who discussed, among other issues, border security. During the session, where Trump freely hopped around from position to position on a range of topics, seemingly unsure of what his own agenda is, he walked back his promise of a comprehensive wall.

“We don’t need a wall where you have rivers and mountains and everything else protecting it,” Trump announced. “But we do need a wall for a fairly good portion.”

On Wednesday, Sen. John Kennedy (R-LA) conceded to CNN’s Chris Cuomo that he no longer understands what Trump means when he says he wants to build a wall:

CUOMO: Do you think you know what the president means when he says he wants a wall?

KENNEDY: I do not.

CUOMO: Does that bother you that we don’t know?

KENNEDY: I’ve seen his proposal. We’ve got about 1,900 miles of border with Mexico. About a third of them have a wall now, or a fence, or what someone could call a wall. The president’s proposal is to wall off another third. The folks at Homeland Security tell me it will help, not just in term of people coming here illegally, but in term of guns, sex trafficking.

CUOMO: When you say his proposal, senator, what are you talking about? Because during the campaign he said a wall all the way, new, bricks and mortar, I can build it, it will only take a year. And then yesterday he seemed to back off to the mainstream position, of experts and people who security the border who say, “Some places a wall, some places a fence.” That’s how you got the Democrats to sign on for funding for these types of security measures, sensors and otherwise, with the Gang of 8.

KENNEDY: The proposal I’m responding to, Chris, is from Homeland Security. They want about 600 miles of wall. It’s $25 million a mile. And we need to talk about that. We built 2,700 miles of walls along every interstate in American for about $4.5 billion. So $18 billion for 600 miles? I need to ask a few questions about that.

Reminder: Trump campaigned on the promise that Mexico would pay for the wall.

Mexico is definitely not paying for any wall.