When U.S. President Donald Trump and Chinese leader Xi Jinping meet in Beijing in mid-May, the visit will mark the next step in trying to steady the world’s most consequential relationship. The last time the two leaders met face-to-face, in South Korea late last year, Trump described the meeting as a convening of the “G-2.” It may have been just an offhand remark, but the reference—suggesting that Washington and Beijing would jointly set the terms of the regional and even global order — reverberated around the region. U.S. allies such as Australia and Japan immediately wondered whether Washington was abandoning them and granting Beijing greater influence. In the past, neither China nor the United States embraced the G-2 label. U.S. officials balked at giving China symbolic parity, while Beijing suspected Washington was trying to get China to accept international burdens that it did not want to shoulder.…