A Democratic witness at the House Judiciary Committee's impeachment hearing is apologising for bringing up the name of President Donald Trump's 13-year-old son, Barron.

Stanford law professor Pamela Karlan said Wednesday that ‘’it was wrong of me to do that,'' adding, ‘’I do regret it.''

Karlan's apology came after she faced a firestorm of criticism from Republicans, including first lady Melania Trump, who tweeted that "a minor child deserves privacy and should be kept out of politics."

Karlan had joked earlier Wednesday that the president can “name his son Barron, he can't make him a baron." Karlan was trying to make a point that Donald Trump is a president, not a king.

Melania Trump said Karlan "should be ashamed of your very angry and obviously biased public pandering, and using a child to do it."'