WATCH: Axios reporter busts Ted Cruz for lying that Trump never made promises on the national debt

In a new interview with Axios reporter Jonathan Swan, Sen. Ted Cruz (R-TX) tried to defend President Donald Trump's lack of concern for the national debt — an issue Cruz has spent years claiming was one of the most pressing on Capitol Hill — and almost immediately got caught in a lie.

"[Trump official] Mick Mulvaney had a great quote," said Swan. "He said, you know, 'The deficit's the worst thing in the world when Barack Obama's president, but Donald Trump came in and we're not so worried about that anymore.' He's right, isn't he?"

"So look, I'm very worried about the debt," said Cruz. "And I'm worried about it under Trump. Now, to be fair, Trump didn't campaign on cutting the debt."

"He did," cut in Swan. "He said he was going to eliminate the national debt in 8 years." Trump did indeed make that promise.

"He also said something, what is it, 'I'm the king of debt,' in 2016." replied Cruz. Trump did say that, but Cruz was taking him out of context — by "king of debt," he meant he's such an expert in debt that as president, he could negotiate with America's creditors and cut America's obligations dramatically. This hasn't happened, partly because it isn't constitutional.

Watch below: