Unstoppable rhetoric collided with immovable facts on “Fox News Sunday,” as White House senior policy adviser Stephen Miller defended President Trump’s national emergency declaration and invoked the potential for a veto if Congress disapproves in an interview with Chris Wallace.

The segment focused on the limits of presidential powers to circumvent Congress and procure funds to build 230 miles of barriers along the southern border. Miller described an onslaught of drugs and migrants flowing over the border as justification for the emergency declaration.

Yet, like a small army of fact-checkers have noted before, Wallace told Miller the vast majority of hard drugs seized by Customs and Border Protection are captured at points of entry, not between them, and unlawful migration over the border has fallen 90 percent since 2000.

So what crisis is the wall supposed to solve? In shades of former defense secretary Donald H. Rumsfeld’s “unknown unknowns” theory, Miller invoked what could not be demonstrated by his own administration’s statistics.

“You don’t know what you don’t know, and you don’t catch what you don’t catch,” Miller told Wallace. “But as a matter of national security, you cannot have uncontrolled, unsecured areas of the border where people can pour in undetected.”

The segment took a tense turn after Wallace pressed Miller, a self-proclaimed constitutional conservative, over measures designed to block the president from obtaining funds outside Congress.

That wasn’t an issue, Miller said: “Congress in 1976 passed the National Emergency Act and gave the president the authority, as a result of that, to invoke a national emergency in many different circumstances, but among them the use of military construction funds.”

And the military, conveniently, has already been deployed to the southern border, Miller noted, and a wall is needed to “secure those areas where they’re patrolling.”

In other words, troops were deployed to help harden the border and now need barriers to keep them safe from a threat Miller did not describe.

President Trump declared a national emergency to secure funding for a wall at the U.S.-Mexico border. (Joy Sharon Yi/The Washington Post)

Still, the move lacks precedent, Wallace said, in how Trump has sought to secure his funds. Miller repeatedly refused to acknowledge it has not happened before and tried to fire back with a question of his own.

Wallace sailed past the dodge.

“Then answer my question, can you name one case where a president has asked Congress for money, Congress has refused, and the president has then invoked national powers to get the money anyway?”

Miller responded: “Well this current situation —”

Wallace interjected again. “Just yes or no, sir.”

Miller answered “no” in a quick back-and-forth before moving to emergency declarations involving Zimbabwe as an example of overzealous use of authority — even though the 2003 measure against associates of despot Robert Mugabe was extended by Trump himself in March.

Miller ended the segment with a portent of even more challenging political maneuvering.

By September 2020, Miller said, “hundreds of miles” of new barriers will have been built along the border.

And he suggested that if Congress passes a resolution disapproving of the emergency, Trump would probably veto it. “He’s going to protect his national emergency declaration, guaranteed. … If the president can’t defend this country, then he cannot fulfill this constitutional oath of office.”

The segment ended. Wallace, in a flash of understatement, bid his guest farewell.

“It’s always good and always challenging to talk to you,” Wallace said.

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