WATCH: CNN panel melts down as Trump defender Steve Moore goes on unhinged rant about 'sanctuary cities'
Supply side economist Stephen Moore (Screen cap).

Economist Stephen Moore espoused his staunch defense of Donald Trump on Thursday -- and led to an on-air meltdown as host Erin Burnett and his fellow guest hit back at his claims about the proposed Mexican border wall.

After claiming he "doesn't agree entirely" with the president, the former Trump campaign economic adviser claimed Democrats are "out of touch" with Americans and that most "major Democratic cities" are "sanctuary cities."

"Every major Democratic city in the country, my hometown of Chicago, Boston, San Francisco, Los Angeles, they're all sanctuary cities, basically telling illegal immigrants, 'Come to San Francisco, come to Boston, come to Chicago,'" Moore claimed. "What kind of border security is that?"

"Sanctuary cities -- that whole issue is played out," The Nation's Joan Walsh said.

"Wait a minute, how do you defend that?" Moore said -- but Walsh wasn't having it.

"Don't interrupt me, please," she said. "You asked me a question, don't interrupt me."

The economist continued repeating "how do you defend that" when the host stepped in.

"Let her answer the question," Burnett said.

Walsh began responding with a comment about the shutdown as Moore began laughing at her.

"Stop it!" she said.

Watch below: