The Trump administration is asking for $18 billion in spending over 10 years to extend the southern border wall with Mexico, according to the Associated Press.

Why it matters: Per the AP, this is one of the administration's "most detailed blueprints" of Trump's plan for the border wall, which was a staple of his campaign. The request comes amid Congressional negotiations on what to do about immigrants who were illegally brought to the U.S. as children, known as "dreamers."

• The wall will be "first and foremost" in any dreamer-related legislative package, Homeland Security Secretary Kirstjen Nielson tells the AP.

Go deeper: Trump's evolving plans for the border wall.