China’s muted reaction over a U.S. military flight to Taiwan prompted criticism from nationalists online, underscoring the pressures on President Xi Jinping to follow through on heated "red line” rhetoric.

The U.S. Air Force C-17 cargo plane made a three-hour stopover in Taipei on Sunday to carry a bipartisan congressional delegation visiting Taiwan. Three U.S. senators — Democrats Tammy Duckworth and Chris Coons and Republican Dan Sullivan — met with Taiwanese President Tsai Ing-wen and announced plans to donate 750,000 COVID-19 vaccine doses to help alleviate its shortage of shots.

Although Taiwanese media reported that it was the first C-17 visit since at least 1995, the Chinese response was relatively measured. State media, including the official Xinhua News Agency, didn’t report on the trip while the Foreign Ministry and Taiwan Affairs Office didn’t immediately respond to a request for comment.