President Donald Trump called for the firing of longtime New York Times columnist Paul Krugman in a tweet on Sunday.

The tweet was the latest escalation in an ongoing war of words between the 45th president and the Nobel Prize-winning economist.

Krugman responded in a tweet Sunday and said it was "kind of amazing how much rent-free space I seem to occupy in Trump's head."

Read more on Business Insider's homepage.

President Donald Trump called for the firing of New York Times columnist and Nobel Prize-winning economist Paul Krugman in a tweet on Sunday in the latest escalation of the war of words between the two.

"Paul Krugman is a lightweight thinker who doesn't have a clue," the president tweeted Sunday morning. "Caused huge economic damage to his follower's pocketbooks. He, and others, should be fired by @nytimes!"

The tweet included a video shared by libertarian radio host Larry Elder that showed economist Thomas Sowell talking about the economy under the Trump administration, which specifically targeted Krugman's past predictions.

"The economy is booming in a way that no one had predicted," Sowell said in the clip. "People like Paul Krugman were saying that when Trump gets in, the economy is going to tank. No, the economy hit new highs."

The video clip of Sowell seems to be taken from a November 2018 interview posted by the Hoover Institute, a public policy think tank at Standford University, where Sowell is a fellow.

Krugman responded to Trump on Twitter later Sunday.

"I usually ignore Twitter trolls, but it's kind of amazing how much rent-free space I seem to occupy in Trump's head," Krugman tweeted after the president called for him to be fired. "Shouldn't he be focused on threatening Adam Schiff?"

The president often directs his ire toward Schiff, a Democrat from California and the chairman of the House Judiciary Committee, over his handling of Trump's impeachment.

Besides the 2018 video shared by Elder, there wasn't a clear indication of what, exactly, set Trump off Sunday, though Krugman's most recent January 23 column published by The New York Times criticizes Trump for "abusing his tariff power."

As Markets Insider reported, Sunday wasn't the first time the president had attacked Krugman, the president also lashed out at the New York Times columnist in a tweet January 20.

"If you listened to the flawed advice of @paulkrugman at the @nytimes, a newspaper that was going broke until I came along, you would have entirely missed the RECORD BREAKING Stock Market (and other) numbers produced since Election Day, 2016," Trump tweeted last week. "Sorry, those are the FACTS....."

Krugman, a longtime critic of the 45th president, predicted that his election in 2016 would lead to global economic fallout, believing that Trump would tighten the Federal Reserve. The Nobel Prize winner has regularly authored unfavorable columns for The New York Times throughout the Trump presidency and claimed that any economic growth that has occurred under him was a result of the policies of the previous administration.

The president has fired back against Krugman — also on Twitter — at several points over his administration, including in April and November last year.

While their feud has lasted years, Markets Insider noted that Krugman's prediction of economic disaster under Trump has not so far not been realized.

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