Until it was shot down, it appeared to be floating peacefully in US airspace. But on the ground, the alleged use of a spy balloon triggered a diplomatic maelstrom, which experts say has undermined efforts to repair US-China relations.“This incident is incredibly embarrassing for Beijing. It reinforces concerns that most Western nations justifiably harbor about China's grand ambitions for power," Craig Singleton, senior China fellow at the Foundation for Defense of Democracies, a think tank for China, told NBC News on Saturday. Washington, DC. He added that Secretary of State Antony Blinken's decision on Friday to indefinitely postpone his visit…