U.S. President Trump said last week that he wants South Korea, a key American ally in Asia, to foot the bill for the $1 billion THAAD missile defense system whose deployment angered China because it undermines the country’s strategic security interests and is unhelpful for ensuring peace and stability on the Korean Peninsula. “I informed South Korea it would be appropriate if they paid,” Trump said in an interview with Reuters on April 27. “It’s a billion-dollar system,” he added.

South Koreans were caught off-guard by his comments. “Is South Korea a colony that has to cough up cash whenever the U.S. wants it to?” Park Hee-ju, an anti-THAAD activist, told the Hankyoreh newspaper. But Trump has long said that the U.S. shouldn’t be the one who foots the bill for protecting South Korea.

Trump’s recent comment about THAAD isn’t the first time he has seemed to openly question the relationship with South Korea. “How much is South Korea paying the U.S. for protection against North Korea?” Trump asked in a March 2013 tweet. “NOTHING!” he added. In one tweet, Trump called South Korea “our economic competitor”; and in another, he tried to make a point by asking how much “very wealthy South Korea” is paying the U.S. for protection against North Korea.

In April 2013, Trump shared a video on YouTube titled, “From the Desk of Donald Trump: South Korea,” in which he slammed South Korea for free riding on the backs of American taxpayers. “I keep asking. How long will we go on defending South Korea from North Korea without payment,” Trump said in the video. “They think we’re stupid,” he added. Following the video, Trump continued his verbal attack on South Korea. The U.S. “must stop being stupid,” he wrote in one tweet.

On Weibo, Chinese netizens are amused by the public spat between two so-called allies over who should foot the bill. Netizen dusijia0925 called the situation an example of South Korea “dropping a rock on its own foot.” Netizen fandudamengzhu wished Trump the best of luck on his next move, but warned China to never put its security in the hands of others. Some netizens joked that payment was due on delivery and that returns are not accepted, referring to reports that parts of the system have been moved into site and is operational with “initial intercept capability.” Netizen ibilin suggested tacking on another bill, saying South Korea should pay China $1 billion for the development of an “anti-THAAD system.” One netizen wrote, “Don’t anger China,” adding that doing so would only bring about even more economic loss, referring to reports that the number of Chinese tourists to the country has dropped amid tensions. China is an important economic partner of South Korea. But one netizen called the move “a trap,” suggesting it was Trump’s attempt to shakedown South Korea. “Increase tension on the Korean Peninsula and then demand protection money,” netizen mingmingyue_31850 wrote on Weibo.