CNBC anchor John Harwood slammed GOP presidential candidate Donald TrumpDonald TrumpSt. Louis lawyer who pointed gun at Black Lives Matter protesters considering Senate run Chauvin found guilty as nation exhales US says Iran negotiations are 'positive' MORE's policies as fantasies Wednesday, and asked if he is running "a comic book version of a presidential campaign."
Harwood, a moderator in Wednesday's Republican presidential debate, said Trump's plans on immigration and taxes are not believable.
Trump, the Republican front-runner, countered that CNBC personality Larry Kudlow "loves my tax plan." 
And on the subject of border security, Trump said building a wall across the Mexican border is "something that can be done."
"They built the Great Wall of China. That's 13,000 miles. Here we actually need 1,000," he said. "We can do a wall.
"People say, 'oh how are you gonna get Mexico to pay?' " the billionaire businessman added. "A politician cannot get them to pay. I can."
Harwood challenged Trump yet again on his tax plan.
"I talked to economic advisers who have served presidents of both parties," he said. "They said you have as much chance of cutting taxes that much without increasing the deficit as you would of flying away from that podium by flapping your arms."
"Then you have to get rid of Larry Kudlow, who sits on your panel, who is a great guy, who came out the other day and said 'I love Trump's tax plan,' " Trump responded.