Vice President Mike Pence stayed silent during a meeting between President Donald Trump and Democratic leaders that turned into a debate over funding for a border wall.

House Speaker-designate Nancy Pelosi, Senate Minority Leader Chuck Schumer, and Trump exchanged heated words while Pence sat silent.

Pence has previously committed himself to securing funding for a border wall, but he has also received pressure from lawmakers to avoid a shutdown that's looming under a December 21 spending bill deadline.

A photo op ahead of a meeting on the federal spending bill needed to keep the government open turned into an all-out public debate Tuesday. But one participant — Vice President Mike Pence — sat on the sidelines.

What was meant to be a friendly preview of negotiations between House Speaker-designate Nancy Pelosi, President Donald Trump, Senate Minority Leader Chuck Schumer, and Pence devolved into a shouting match over funding for Trump's border wall, with heated exchanges among Trump, Schumer, and Pelosi.

The only one who wasn't participating was Pence, who barely attempted to get a word in and came off as uncomfortable. He moved his head to follow each speaker while maintaining a stern expression and at only one point shifting to adjust his jacket.

Trump engaged in heated exchanges with Senate Minority Leader Chuck Schumer and House Speaker-designate Nancy Pelosi. AP Photo/Evan Vucci

Read more: The Trump administration paid a private company $13.6 million to recruit thousands of Border Patrol agents, and they've hired 2 so far

In the meeting, Trump said he would be "proud" to shut down the government if Democrats would not help fund his proposed border wall between the US and Mexico, which was part of his campaign platform and has been a persistent sticking point for him in office. Trump issued a similar threat in 2017.

"I am proud to shut down the government for border security," Trump said. The deadline to come to an agreement before a shutdown is December 21.

Pence is seemingly stuck in the middle of the funding debate. On the one hand, Pence has chosen to support Trump's border wall. In February, Pence remained vague on the wall, committing to securing funding for a barrier, but not explicitly endorsing a physical wall.

But in March, an email from Trump's 2020 campaign signed by Pence announced the launch of the "Official Build the Wall Petition," saying "this administration is 100% committed to building a wall along the southern border of the United States of America."

Pence has also reportedly received pressure from Republican members of Congress to keep the government open. The Hill reported that on November 27, Republican senators warned Pence during a lunch that a shutdown should be avoided "at all costs," according to Republican Sen. Shelley Moore Capito.

Republican legislators are reportedly committed to a $5 billion allocation for border security. A complete border wall is estimated to cost upward of $25 billion.

You can watch the entire exchange here:

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