When it comes to Taiwan — long seen as the issue most likely to drag the U.S. and China into war — every word matters. And lately U.S. President Joe Biden has been flubbing his lines regularly.

After reassuring Chinese leader Xi Jinping that the U.S. doesn’t take a position on Taiwan’s sovereignty in a Monday virtual summit, Biden one day later described the island as "independent” to reporters. The president quickly walked back the comment, saying he was referring only to the democratically ruled island’s need to make its own decisions, and not asserting its independence — China’s oft-stated red line for an invasion.

It was at least the fourth time in as many months that Biden or his aides needed to clarify a remark he’d made on Taiwan, which Xi’s Communist Party claims even though it has never ruled the island. The sensitivity around language regarding Taiwan reflects the tremendous stakes involved: Any real shift in policy risks sparking a conflict between two nuclear powers.