Senior White House adviser Stephen Miller said Sunday that President Donald Trump will defend his decision to announce a national emergency at the U.S.-Mexico border, in spite of opponents launching political and legal battles aimed at stopping the move.

What are the details?

On Friday, President Trump announced he would sign a declaration using executive authority to circumvent Congress and redirect billions of dollars to secure the border wall funding he had requested in last week's budget deal. His decision was met with immediate threats of lawsuits and legislation challenging the action.

A number of opposition groups and state attorneys general have promised to pursue an injunction of the emergency declaration in court, while Democrats are drafting a resolution seeking to block it under the National Emergencies Act.

Speaking on "Fox News Sunday," Miller defended the president's executive authority to declare an emergency and dismissed both threats, telling host Chris Wallace, "Obviously, the president is going to protect his national emergency declaration. He's going to protect his national emergency declaration — guaranteed. But the fact that they're even talking about a resolution of disapproval shows you this is a statutory issue and a statutory delegation that Congress made."

Miller also suggested that the president would likely veto any legislation from Congress attempting to override the national emergency declaration.

Wallace and Miller engaged in a back-and-forth over the constitutionality of the action, with Miller arguing:

This would not be even an issue if the president was invoking that statute to support some foreign adventure overseas. You and I both know that presidents for years have engaged in one military adventure after another, not to mention the fact that we do operations to destroy drug fields in foreign lands in Afghanistan or in Colombia. And we can't even deal with the criminal cartels operating on our border?

Anything else?

Responding to Wallace's question about how many miles of barriers the administration will build with the $8 billion it plans to redirect, Miller said, "You're going to see probably a couple hundred miles [of wall] in time, I would say, by the end of the next appropriation cycle. Altogether in terms of what we already have underway, what's underway right now, and then what we're going to complete."