Trump’s mocking of Thunberg, who has been diagnosed with Asperger syndrome, as having an “Anger Management problem” drew widespread umbrage from Democrats who accused the president of bullying a teenager. His tweet came just a week after Republicans cried foul when a university professor made a joke referencing Barron Trump, the president’s 13-year-old son, during impeachment testimony.

“So ridiculous,” Trump wrote in a tweet about Thunberg’s Time honor, suggesting that one of the world’s most powerful voices for the environmental movement “go to a good old fashioned movie with a friend. Chill Greta, Chill!”

The message was one of more than 100 tweets or retweets the president sent on Thursday to more than 67 million followers, the second time he has surpassed that number of posts this week. Trump’s increasing use of social messaging — mostly focusing on defending him in the House Democrats’ impeachment probe — suggest the president is eager to rally his conservative base at a politically perilous moment.

But his targeting of a teenager went beyond his usual broadsides directed at his political adversaries in Washington.

“He can’t bully @SpeakerPelosi, so he’s trying to bully a teenager,” Senate Minority Leader Charles E. Schumer (D-N.Y.) wrote on Twitter. He added the hashtag #BeBest, the name of first lady Melania Trump’s anti-online bullying campaign aimed a young people.

Sen. Richard J. Durbin (D-Ill.), the Senate’s second-ranking Democrat, reacted to Trump’s insults by imploring him to “stop slinging insults at a teenager & start acting like an adult.”

As other political leaders, including Democratic presidential candidate Joseph Biden, rushed to her defense, Thunberg offered a sly rejoinder to Trump, 73, by updating her Twitter profile to describe herself as: “A teenager working on her anger management problem. Currently chilling and watching a good old fashioned movie with a friend.”

Trump’s attack on Thunberg, which came in response to a tweet congratulating her by Roma Downey — an actress who is married to Mark Burnett, a producer on Trump’s previous reality television series “The Apprentice” — marked the second time he has publicly belittled her.

During the U.N. General Assembly in September, Trump tweeted sarcastically that Thunberg seemed like “a very happy young girl … So nice to see!” after a video of her impassioned — and somewhat fatalistic — plea to global leaders about the dangers of climate change went viral.

The president has called climate change a “hoax,” and his administration has relaxed carbon emissions regulations on power plants and the auto industry and begun withdrawing the United States from the Paris climate agreement, signed by every other nation.

Time’s selection of Thunberg as its 2019 honoree has prompted praise among many liberals, but the president’s conservative allies have joined him in denouncing the decision.

Donald Trump Jr. invoked a line from Thunberg’s U.N. speech in asking Time, “How dare you?” — and he suggested the pro-democracy protesters in Hong Kong would have been the better choice. Charlie Kirk, president of Turning Point USA, a conservative student group, called Thunberg, who began skipping a day of school to draw attention to the climate issue, a “perpetual truant” and declared Trump should have taken the honor.

The rush among Trump allies to bash Thunberg marked a striking contrast to their professed outrage last week when Pamela Karlan, a Stanford University law professor, had invoked Barron Trump’s name during her testimony before the House Judiciary Committee’s impeachment hearing. In making a point that Trump is not a dictator, Karlan quipped that “while the president can name his son Barron, he can’t make him a baron.”

“Pamela Karlan, you should be ashamed of your very angry and obviously biased public pandering, and using a child to do it,” the first lady wrote in a tweet.

Yet on Thursday, Melania Trump and others who had scolded Karlan, including White House press secretary Stephanie Grisham and several GOP lawmakers, were silent about the president’s attack on Thunberg. White House officials, including Grisham, did not respond to a request for comment, and messages to the House offices of Reps. Matt Gaetz (R-Fla.) and Mike Johnson (R-La.), who denounced Karlan’s remarks, went unanswered. A Trump campaign spokeswoman also did not respond to an email.

Some conservatives have argued that because Thunberg, unlike Barron Trump, is a political activist, she is fair game for criticism from those whose policies she has campaigned against and whose moral values she has questioned.

“The difference between the two cases should be plain: Greta, or her handlers, have placed her directly in the public spotlight for explicitly political reasons,” said Daniel Lee, a National Review contributor who has compared Thunberg to Samantha Smith, an American girl who campaigned against nuclear weapons in the 1980s. “Barron is a noncombatant, having no intentional public footprint at all.”

Lee added of Trump: “Personally, I’d rather see him include in his criticism the people who are putting her in this very public position, but not criticizing her at all just plays into the hands of the activists using her youth and innocence to ward off criticism of their goals.”

But Trump has not engaged Thunberg on specific policy points but rather made personal attacks. During his presidency, Trump has shown little restraint mocking those with disabilities — or suggesting, without evidence, that his targets are mentally ill.

During his presidential campaign, he appeared to mock a disabled reporter from the New York Times during a rally, although he denied having done so. He has called actress Rosie O’Donnell a “mentally sick woman,” and questioned the mental capacity of two fellow New Yorkers — former state attorney general Elliot Spitzer and former Democratic congressman Anthony Weiner.

Trump referred to his former Attorney General Jeff Sessions as a “mentally retarded southerner,” according to a book by the journalist Bob Woodward.

“What kind of president bullies a teenager? @realDonaldTrump, you could learn a few things from Greta on what it means to be a leader,” Biden wrote in a tweet. The former vice president has been angered over Trump’s criticism of his adult son Hunter’s role on the board of a Ukrainian energy company, which had prompted the president to privately press that country’s president over the summer to launch an investigation into the Bidens — a move that led to the House impeachment probe.

In explaining Time’s choice of Thunberg as Person of the Year, the magazine’s editor in chief, Edward Felsenthal, said Wednesday that “she became the biggest voice on the biggest issue facing the planet this year, coming from essentially nowhere to lead a worldwide movement.”

Trump, who was among the five finalists for the distinction this year, has had a long obsession with the magazine’s selections, dating back before he became president. Fake 2009 Time covers showing Trump as person of the year and touting his days as host of “The Apprentice” have been found hanging in several of his golf clubs.

In 2015, as a candidate for president, Trump took to Twitter to complain after Time chose German Chancellor Angela Merkel for her leadership in the Greek debt crisis and European migrant crisis. Time did honor Trump in 2016 after he won the White House by defeating Democrat Hillary Clinton, prompting a tweet that called the selection “a great honor.”

A few hours after Trump’s tweet Thursday, his campaign sent out an altered image of Time’s cover with Trump’s head superimposed in place of Thunberg’s and a tag­line promoting the “power of promises kept.”

Kim Bellware and Hannah Knowles contributed to this report.