© Matt McClain/The Washington PostPamela S. Karlan.
A reference by Stanford professor Pamela Karlan to the president's youngest child during Wednesday's House Judiciary Committee impeachment hearing drew swift and angry rebukes from President Trump's campaign and his spokeswoman.
Karlan said Trump was wrong when he once claimed the Constitution gave broad and unchecked power, like a king.
"I'll just give you one example that shows the difference between him and a king, which is the Constitution says there can be no titles of nobility," she said. "So, while the president can name his son Barron, he can't make him a baron," she said.
White House press secretary Stephanie Grisham called it a "classless move."
"Prof Karlan uses a teenage boy who has nothing to do with this joke of a hearing (and deserves privacy) as a punchline. And what's worse, it's met by laughter in the hearing room. What is being done to this country is no laughing matter," she said on Twitter.
"Every Democrat in Congress should immediately repudiate Pamela Karlan and call on her to personally apologize to the President and the First Lady for mocking their son on national TV," the Trump campaign said in a statement.
Republicans have sought to call Hunter Biden, who served on the board of Ukrainian energy company Burisma Holdings, as a witness, but Democrats have refused, and some have criticized the request by the GOP.