The White House defended President Donald Trump's recent attack on teenage climate activist Greta Thunberg on Twitter because Thunberg "travels the world giving speeches."

"So ridiculous," Trump tweeted in response to Thunberg being honored as Time's 2019 Person of the Year. "Greta must work on her Anger Management problem, then go to a good old fashioned movie with a friend! Chill Greta, Chill!"

Previously, the First Lady sharply criticized a witness in Trump's impeachment inquiry for making a play on words out of her 13-year-old son Barron's name.

White House Press Secretary Stephanie Grisham suggested in a statement that it was fair for Trump to attack Thunberg because she is a public figure.

"Their son is not an activist who travels the world giving speeches. He is a 13-year-old who wants and deserves privacy," Grisham said.

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White House Press Secretary Stephanie Grisham defended President Donald Trump on Friday for his recent Twitter attack on climate activist Greta Thunberg, saying the harsh criticism of the teenager was fair game because she "travels the world giving speeches."

Trump was passed over for Time Magazine's 2019 Person of the Year in favor of Thunberg, a 16-year-old Swedish student who has risen to international fame for her powerful climate activism.

In the early hours of Thursday morning, Trump tweeted a personal attack on Thunberg in response to her Time cover. "So ridiculous," he wrote. "Greta must work on her Anger Management problem, then go to a good old fashioned movie with a friend! Chill Greta, Chill!"

Thunberg immediately responded in kind by changing her Twitter bio to read, "A teenager working on her anger management problem. Currently chilling and watching a good old fashioned movie with a friend."

Many questioned why First Lady Melania Trump did not condemn Trump's public attack on Thunberg, given that she runs an anti-cyber-bullying initiative called #BeBest, and sharply criticized a witness in Trump's impeachment inquiry for making a play on words out of her 13-year-old son Barron's name.

In a statement to CNN's Kate Bennet, White House Press Secretary Stephanie Grisham emphasized that the First Lady and the president "communicate differently," and suggested that it was fair for Trump to attack Thunberg because she is a public figure.

At a December 4 hearing in the House Judiciary Committee, Stanford University Law Professor Pamela Karlan invoked Barron's name in making a point about the limits of the president's powers under Article II of the US Constitution. Trump has previously claimed that Article II "gives me the right to do whatever I want."

"The Constitution says there can be no titles of nobility, so while the president can name his son Barron, he can't make him a baron," Karlan said in explaining Article II.

While Karlan's remark clearly wasn't meant as an attack on the president's son, Melania responded by criticizing Karlan for "pandering" and said she should be "ashamed."

"A minor child deserves privacy and should be kept out of politics," Melania said. "Pamela Karlan, you should be ashamed of your very angry and obviously biased public pandering, and using a child to do it."

Read more:

Michelle Obama sent Greta Thunberg a public message of solidarity following Trump's vitriolic attack on her

Trump attacked Greta Thunberg after she beat him to be named Time's Person of the Year, telling her to abandon her activism and watch a movie instead

Melania Trump says impeachment witness who brought up her son Barron in testimony should be 'ashamed'