President Trump's proposed border wall has long been a rallying cry for his supporters. Aides say Trump's views on the wall have evolved over time, but the president insists his plan is still rock solid.
MARY LOUISE KELLY, HOST: President Trump says his commitment to a border wall remains rock solid. He appears to be pushing back today against comments from his chief of staff that the president's feelings on the wall have evolved over time. In a tweet this morning, Trump insisted, quote, "the wall is the wall. It has never changed or evolved." NPR's Scott Horsley reports.</s>SCOTT HORSLEY, BYLINE: From the moment he began running for president two and a half years ago, Donald Trump's border wall has been a central feature of his campaign.</s>PRESIDENT DONALD TRUMP: Nobody builds walls better than me. Believe me. And I'll build them very inexpensively.</s>SCOTT HORSLEY, BYLINE: This is from the president's 2015 kickoff announcement in Trump Tower, the one where he denounced Mexican border crossers as rapists and drug dealers.</s>PRESIDENT DONALD TRUMP: I will build a great, great wall on our southern border, and I will have Mexico pay for that wall. Mark my words.</s>SCOTT HORSLEY, BYLINE: Never mind that illegal border crossings had already fallen 75 percent in the last 15 years or that most illicit drugs are smuggled through legal ports of entry. The builder-turned-politician had struck a nerve, and Trump's border wall quickly became a rallying cry at campaign events around the country...</s>PRESIDENT DONALD TRUMP: Build the wall. Build the wall. We will.</s>UNIDENTIFIED CROWD: Build the wall. Build the wall.</s>SCOTT HORSLEY, BYLINE: ...As always with the call and response.</s>PRESIDENT DONALD TRUMP: Who's going to pay for it?</s>UNIDENTIFIED CROWD: Mexico.</s>PRESIDENT DONALD TRUMP: One hundred percent, OK?</s>SCOTT HORSLEY, BYLINE: Mexico's president made it crystal clear his country would not pay for the wall. He even canceled an early meeting with Trump to drive that point home. The two men later spoke by telephone, and Trump urged his counterpart not to call his bluff so publicly.</s>SCOTT HORSLEY, BYLINE: Funding for the wall is now one of the sticking points in congressional negotiations over spending and immigration. Democratic Senator Patrick Leahy of Vermont grilled the homeland security secretary earlier this week.</s>PATRICK LEAHY: Do you know whether we have arrangements with Mexico to pay for it?</s>KIRSTJEN NIELSEN: I know that we have arrangements with Mexico to secure our border.</s>PATRICK LEAHY: Do we have arrangements with them to pay for the wall as President Trump promised the American people they would do?</s>SCOTT HORSLEY, BYLINE: In ducking the question, Secretary Kirstjen Nielsen made it plain the administration doesn't have an actual plan to recover the wall's cost from Mexico.</s>KIRSTJEN NIELSEN: How do you mean pay, Sir? Do you mean through fees? Do you mean through - there's a variety of ways.</s>PATRICK LEAHY: Well, usually when something is paid for, you pay for it with money.</s>SCOTT HORSLEY, BYLINE: The White House briefly floated a plan to pay for the wall by taxing imports from Mexico, effectively shifting the cost to U.S. consumers. Republican Senator Lindsey Graham quickly shot down that idea, tweeting, any policy that drives up the cost of Corona, tequila or margaritas is a big-time bad idea - mucho sad. The White House has also suggested that NAFTA negotiations with Mexico could indirectly produce revenue for the wall.</s>SCOTT HORSLEY, BYLINE: For now, though, U.S. taxpayers are on the hook for anything that's built. The administration's asking for $18 billion over the next 10 years, though Trump said last week the wall shouldn't cost that much.</s>PRESIDENT DONALD TRUMP: I like to go under budget, ahead of schedule.</s>SCOTT HORSLEY, BYLINE: Trump has also acknowledged the wall might not need to be a concrete barrier in its entirety. Fencing could work in some areas. And it doesn't have to stretch along the whole 2,000-mile border.</s>PRESIDENT DONALD TRUMP: Because of mountains and rivers and lots of other things. But we need a certain portion of that border to have the wall. If we don't have it, you could never have security.</s>SCOTT HORSLEY, BYLINE: White House chief of staff John Kelly told Fox News this week the president really wants to wall off only about 800 miles of border.</s>MARY LOUISE KELLY, HOST: He has evolved in the way he's looked at things. Campaign to governing are two different things, and this president is very, very flexible in terms of what is within the realm of the possible.</s>SCOTT HORSLEY, BYLINE: Trump is still in campaign mode on Twitter, though, making the case for his wall. While critics have dismissed the proposal as a 14th century solution to a 21st century problem, the border wall remains a potent symbol as well as a stumbling block to congressional compromise. Trump tweeted this morning, if there is no wall, there is no deal. Scott Horsley, NPR News, the White House.