The Trump administration has continued its public fight over the border wall, with White House senior adviser Stephen Miller telling CBS that President Donald Trump is “absolutely” willing to shut down the government on December 21 if Congress refuses to authorize funding for his wall.

Echoing Trump’s own sentiments from Tuesday’s fiery Oval Office debate, Miller told CBS’s Margaret Brennan on Sunday’s Face the Nation that Trump would do “whatever is necessary” — including allowing a partial government shutdown.

“If it comes to it, absolutely. This is a very fundamental issue,” he said. “At stake is the question of whether or not the United States remains a sovereign country. Whether or not we can establish and enforce rules for entrance into our country.”

Miller’s comments come after a very tense, very public week of funding negotiations: A televised White House meeting between Trump, House Minority Leader Nancy Pelosi, and Senate Minority Leader Chuck Schumer Tuesday ended with the president saying he would be “proud” to shut down the government over their refusal to allocate $5 billion in wall funding (the total cost of the wall ranges from $20 billion to $70 billion). “If we don’t get what we want one way or another. ... I will shut down the government,” Trump said.

Schumer held equally firm on NBC’s Meet the Press Sunday, telling Chuck Todd that Trump is “not going to get the wall in any form.”

“We should not let a temper tantrum, threats, push us in the direction of doing something even our Republicans colleagues know is wrong,” the New York Democrat said.

On Face the Nation, Miller implied that refusing to fund the border wall was the same thing as advocating for illegal immigration, saying that Democrats have “a simple choice” between fighting for America’s working class and promoting illegal immigration. There is already $1.6 billion proposed for border security funding — it’s just a number on which Democrats seem unwilling to budge.

Will the government shut down over a couple billion in wall funding?

Trump has already signed a number of government spending bills into law. But Congress is staring down another partial government shutdown deadline on December 21: Seven department spending bills still need to be voted on, and funding for the Department of Homeland Security, which has purview over construction projects on the border, has proven to be the major sticking point.

Democrats have been unwilling to meet Trump’s $5 billion border wall demands, while Trump has been unwilling to offer them anything — other than not shutting down the government.

It’s not the first time Trump has threatened to shut down the government over his border wall — he also threatened a shutdown over summer, although that never went ahead. This shutdown would be the third under Trump; previous shutdowns occurred because Democrats wanted to force a larger Senate debate on immigration and because Sen. Rand Paul (R-KY) was mad about government spending.

It’s not clear if the president and his emissaries are serious or simply posturing this time around.

The Trump administration has been threatening this shutdown for a while now, with White House counselor Kellyanne Conway telling Fox & Friends last month that Trump “is keeping all options open,” when asked about the possibility of a shutdown.

But as Ezra Klein pointed out after the Trump-Pelosi-Schumer showdown, Trump doesn’t actually want the wall as much as he wants a reality show-style fight over it:

[I]t’s the winning, not the wall, that drives him. It’s showing his supporters he’s fighting for them that powers his presidency, not actually getting anything done. Tuesday’s Oval Office meeting was meant to give Trump what he at least thinks he wants — not the wall, but a fight over the wall.

The White House chose to send Miller, a hardline immigration opponent, out to talk on Sunday — and he delivered a hard line (plus some good television).