How Trump finds himself boxed in over the idea of building a border wall

Advisers said the president became absorbed by the idea of a wall because it was the most memorable and tangible promise he made while stumping for the White House in 2016

Before it became the chief sticking point in a government shutdown drama that threatens to consume his presidency at a critical moment, President Trump’s promise to build a wall on the southwestern border was a memory trick for an undisciplined candidate.

As Mr. Trump began exploring a presidential run in 2014, his political advisers landed on the idea of a border wall as a mnemonic device of sorts, a way to make sure their candidate — who hated reading from a script but loved boasting about himself and his talents as a builder — would remember to talk about getting