Matt Schlapp, an ardent supporter of President Donald Trump, lashed out at right-leaning ABC contributor Matthew Dowd on Sunday and demanded that he quit calling him a "liar."

During a panel discussion about President Trump's desire for Democrats to agree to a border wall, Schlapp argued that the Democrats might be "dumb enough to say 'hashtag resistance' all year."

"If they decide to never work with Donald Trump on any issue, that is a political risk that is not wise to take," he insisted.

Dowd, a former speechwriter for President George W. Bush, expressed a different point of view: "I know Matt likes to create a world that is sort of fictional."

"Are you saying I'm a liar, Matt?" Schlapp interrupted, appearing to raise out of his seat. "That's way beyond. I don't need truth serum. I don't need to be lectured by you about being a liar."

"I never called you a liar," Dowd insisted.

"You did! You did in the first segment!" Schlapp exclaimed.

"No, I did not," Dowd replied. "I said if you drank truth serum, you would actually admit [the truth]."

"Clever way of calling me a liar," Schlapp complained, pointing his finger at Dowd.

"The Republicans have passed nothing that is popular with America in 2017," Dowd said, concluding his point. "And I expect them to pass nothing that is popular in 2018. The president is inherently the most unpopular president at this point of any president that we've had."

"The Democrats have a generic ballot lead that is larger than anytime in the last 20 years," he added. "So we're seeing a situation that this huge wave is coming and I don't see a president who's only governed to a base to change that in the course of the next few months."

Watch the video below from ABC.