Just in case someone might have missed it the first three times, President Biden again stated for the record Sunday that the United States would respond militarily to a Chinese invasion of Taiwan. In fact, his response to a hypothetical question from CBS News’s Scott Pelley was more unequivocal than the previous assurances he gave in May of this year, October of 2021 and August of 2021. When Mr. Pelley asked him point-blank, “So unlike Ukraine, to be clear, sir, U.S. forces — U.S. men and women — would defend Taiwan in the event of a Chinese invasion?” Mr. Biden replied, “Yes.” And with that, one more strand of the 50-year-old U.S. approach known as “strategic ambiguity” toward the Taiwan Strait unraveled. The White House’s subsequent official statement that the president’s remark constituted no change in official policy was no more convincing than the walk-backs that followed Mr. Biden’s previous assertions that the United States has a security obligation toward Taiwan that is similar to the one it has to defend NATO allies.