For nearly two years now, citizen, candidate and President Donald Trump has agitated for the means to build a wall on the southern border. Better yet, he told supporters during his campaign, it would be American-made and Mexican-paid -- "believe me."

Now, as Republicans and Democrats on Capitol Hill get down to the gritty business of hashing out a deal to codify protections for Dreamers, the White House is insisting that there can be no agreement, either on the full Dream Act or a revival of former President Barack Obama's stopgap Deferred Action for Childhood Arrivals policy, without a guarantee of new federal funds for "the wall."

That's the official line -- one Trump recited again Wednesday afternoon during a brief question-and-answer session with reporters. The reality, though, as we've seen over the past year, is not quite so simple.

Reversing a reversal

During a rare televised negotiating session Tuesday, Trump suggested in response to a question from California Sen. Dianne Feinstein, a Democrat, that he would be on board with passing a clean Dream Act before progressing to other immigration-related issues -- a position, if actually taken, that would all but eliminate the wall as a negotiating tool.

California Rep. Kevin McCarthy, the House majority leader, sensed danger and quickly jumped in to reroute the conversation.

"Mr. President, you need to be clear, though," he explained. "I think what Senator Feinstein is asking here: When we talk about just DACA, we don't want to be back here two years later. We have to have security, as the secretary would tell you."

And so she did.

Three times in the course of a brief back-and-forth with the skeptical Democratic Rep. Henry Cuellar, Secretary of Homeland Security Kirstjen Nielsen insisted "the wall works."

At least as a political product, there's no debating Nielsen -- "the wall" worked wonders in vaulting Trump above and beyond the 2016 GOP primary field. The pledge has its roots, according to an anecdote from Joshua Green's book, "Devil's Bargain," in a conversation from the summer of 2014, as Trump more seriously considered a run.

"Roger Stone and I came up with the idea of 'the Wall,' and we talked to Steve [Bannon] about it," on-again-off-again aide Sam Nunberg told Green. "It was to make sure he talked about immigration."

It worked. First during a speech to the Iowa Freedom Summit in January 2015. Then again, to a much larger audience that June, when the freshly minted candidate introduced the notion to voters around the country.

"I would build a great wall, and nobody builds walls better than me, believe me," Trump said, "and I'll build them very inexpensively. I will build a great, great wall on our southern border. And I will have Mexico pay for that wall."

For all that followed, those two sentences might represent the purest distillation of Trump's pitch to American voters. Who better to deliver a large-scale border wall, elusive even after the passage of a 2006 law calling for one, than Donald J. Trump, real estate mogul. Even better, he'd make the Mexican government foot the bill. No other line so consistently won candidate Trump such sustained and rapturous approval during what would be more than 16 months on the trail.

A wild night out West

A look back at the scene in Phoenix on the evening of Wednesday, August 31, 2016, tells the story.

JUST WATCHED Donald Trump's entire immigration speech Replay More Videos ... MUST WATCH Donald Trump's entire immigration speech 01:12:44

Trump had spent the past month plummeting in the polls, spurring a campaign shake-up that placed Steve Bannon as its chief executive. Two weeks later, Trump was back in Arizona, where he'd stomped the remaining GOP competition in the March primary.

"We will build a great wall along the southern border," he said to approving roars, which he allowed to build as he patiently stepped back from the podium. "And Mexico will pay for the wall."

His candidacy might have been free fall, written off widely and openly at odds with itself, but the message -- the promise, the broadsides against Mexico -- still resonated deeply with his base of support.

When the pushback got more colorful, and a former Mexican leader used a four-letter word to make clear that his country would not pay for the wall, Trump shot back that any opposition would be met with consequences.

"The wall just got 10 feet taller," he said during a CNN primary debate in February of 2016.

Eleven months later, Trump found himself engaged with a rather different audience -- current Mexican President Enrique Peña Nieto.

A 'private' conversation

The transcript of their January 27 phone call, first revealed by The Washington Post , offered a rare glimpse into Trump's unvarnished calculations. The Mexican leader plainly rejected the idea of his country funding a border barrier, setting up a showdown that Trump was, in his new environs, desperately hoping to avoid.

"The fact is we are both in a little bit of a political bind because I have to have Mexico pay for the wall -- I have to," he told Peña Nieto.

Acknowledging the public impasse, Trump added: "Believe it or not, this is the least important thing that we are talking about, but politically this might be the most important (to) talk about."

Publicly, Trump's straddling of the wall became more pronounced as the demands of his new job -- like passing a budget to keep the government running -- closed in.

On April 23, 2017, he sought to manage expectations in a tweet claiming, "Eventually, but at a later date so we can get started early, Mexico will be paying, in some form, for the badly needed border wall." A day later, Trump told a group of conservative reporters he wouldn't walk away from budget negotiations over a deadlock on border wall funding.

As word of those conversations spread, the President, sniffing out a potential backlash from his base, accused reporters of misrepresenting his position. "Don't let the fake media tell you that I have changed my position on the WALL," he tweeted early on April 25. "It will get built and help stop drugs, human trafficking etc."

Keeping up appearances -- and angling for a deal

In October, as congressional Republicans wrangled with other more pressing political conundrums, the Department of Homeland Security unveiled prototypes at a photo op near the border in San Diego.

BORDER WALL prototypes underway! pic.twitter.com/arFNO80zmO — Donald J. Trump (@realDonaldTrump) October 17, 2017

But as time passes, Trump's rhetoric, even as he insisted again Wednesday that a wall must be part of any DACA deal, has mellowed, somewhat. A more holistic approach, not entirely unlike those embraced by older Washington hands, seems to be the flavor of the day.

Immediately after Election Day, he told Lesley Stahl on "60 Minutes" it could consist of some fencing, in addition to heavier wall.

"I'm very good at this, it's called construction," he told her.

"So part wall, part fence?" she asked.

"Yeah, it could be," he said, "it could be some fencing."

The length has also shrunk since the campaign.

"We don't need a 2,000-mile wall," Trump said Tuesday -- in remarks similar to those he had made in July and again in September -- during bipartisan talks. He'd suggested in those summer comments that the structure needs to be transparent, lest smugglers heave "sacks of drugs over" the top --"60 pounds of stuff" -- and onto unsuspecting American heads.

In addition to possible transparent and fencing portions will be natural barriers already in existence.

"We don't need a wall where you have rivers and mountains and everything else protecting it," Trump added, addressing the roundtable of congressional officials.

"But we do need a wall for a fairly good portion."