President Trump invoked on Sunday past pro-border security comments by two unlikely political adversaries -- Barack Obama and Hillary Clinton -- as the ongoing partial federal government shutdown over border wall funding enters its third week.

In a pair of early-morning posts on Twitter, Trump, who later headed to a meeting with advisers at Camp David to discuss border security, also seemingly addressed reports that the prolonged shutdown will end up costing the government more than the $5 billion he has requested for the wall, writing that in the end, a "properly planned and constructed Wall will pay for itself many times a year!"

Trump's remarks underscored his apparent unwillingnesss to compromise on securing at least some of the border wall funding he has demanded, despite the insistence of House Speaker Nancy Pelosi that Democrats will never pay for a wall. However, in an interview broadcast Sunday on NBC's "Meet the Press," Acting White House Chief of Staff Mick Mulvaney told host Chuck Todd that Trump "was willing to agree, and he mentioned this at the Rose Garden press conference, to take a concrete wall off the table."

Mulvaney had met with senior congressional officials on Saturday to try to make progress on a compromise, although he suggested the encounter had been mostly unproductive.

IN SITUATION ROOM MEETING, SCHUMER, PELOSI INTERRUPT DHS SECRETARY WITHIN 5 SECONDS

"Again, what's driving this is the president's desire to change the conditions at the border," Mulvaney said. "And if he has to give up a concrete wall, replace it with a steel fence in order to do that so that Democrats can say, 'See? He's not building a wall anymore' that should help us move in the right direction."

On Twitter, the president intimated that cynical political considerations were motivating Democrats' rejection of wall funding. Pelosi and other Democrats have suggested they would be willing to fund general border security efforts, but not a wall. (The president has told Democrats the shutdown could last more than a year.)

“'We simply cannot allow people to pour into the United States undetected, undocumented, unchecked...'” Barrack Obama, 2005," Trump wrote on Sunday, quoting the former president in 2005. Then-Sen. Obama made the remarks at a press conference with then-Florida GOP Sen. Mel Martinez, as part of a bipartisan effort to address illegal immigration.

PELOSI TO DHS SECRETARY: 'I REJECT YOUR FACTS'

Obama's full quote at the time: "We simply cannot allow people to pour into the United States, undetected, undocumented, unchecked and circumventing the line of people who are waiting patiently, diligently and lawfully to become immigrants in this country."

"We all agree on the need to better secure the border and to punish employers who choose to hire illegal immigrants," Obama added. "We are a generous and welcoming people, here in the United States, but those who enter the country illegally, and those who employ them, disrespect the rule of law and they are showing disregard for those who are following the law."

Obama went on to advocate for imposing a "hefty fine" on those already in the country illegally, as well as tighter border security measures.

In his post, Trump also provided a partial quote from former Secretary of State Hillary Clinton, emphasizing her support for the Secure Fence Act of 2006. That legislation passed by an overwhelming 80-19 majority, and was backed by Obama, as well.

"I voted, when I was a Senator, to build a barrier to try to prevent illegal immigrants from coming in...” Hillary Clinton, 2015," Trump wrote.

"We’re not doing a wall." — Speaker of the House Nancy Pelosi

At a campaign stop in November 2015, Clinton told a crowd: "I voted numerous times when I was a senator to spend money to build a barrier to try to prevent illegal immigrants from coming in. And I do think you have to control your borders."

Trump continued: "The only reason they do not want to build a Wall is that Walls Work! 99% of our illegal Border crossings will end, crime in our Country will go way down and we will save billions of dollars a year! A properly planned and constructed Wall will pay for itself many times a year!"

Last week, former White House Chief of Staff John Kelly flatly asserted in an interview with The Los Angeles Times that the president's proposed border project "is not a wall" and that all plans for a concrete wall were abandoned long ago -- directly contradicting the White House's repeated claims.

In a series of Twitter posts last month, Trump insisted that "we are not building a Concrete Wall, we are building artistically designed steel slats, so that you can easily see through it." But Kelly's comments were seemingly at odds with the president's multiple tweets calling for "money to finish the Wall," as well as his promises during and after the 2016 presidential campaign.

"To be honest, it’s not a wall,” Kelly said in an interview with The Los Angeles Times. “The president still says ‘wall’ — oftentimes frankly he’ll say ‘barrier’ or ‘fencing,’ now he’s tended toward steel slats. But we left a solid concrete wall early on in the administration, when we asked people what they needed and where they needed it."

Pelosi, after regaining the speakership this week, made clear that no wall of any kind was on the table.

"We’re not doing a wall," Pelosi told reporters. "Does anybody have any doubt about that? We are not doing a wall. So that’s that. It has nothing to do with politics. It has to do with: The wall is an immorality between countries. It’s an old way of thinking [and] it isn’t cost-effective.”

At one point during a meeting at the White House on Wednesday, according to the Wall Street Journal, Pelosi interrupted Homeland Security Secretary Kirstjen Nielsen while she was citing statistics related to the border, including how many criminal illegal immigrants attempted to enter the U.S. last year.

“I reject your facts,” Pelosi told Nielsen.