On a Wednesday evening at Joint Base Andrews, President Trump welcomed China's Xi Jinping with a ceremonial reception that departed from conventional diplomatic custom, choosing a military installation as the stage for a meeting freighted with geopolitical consequence. The summit arrived at a moment when Iran's relationships with both Washington and Beijing cast a long shadow over the region, and the question of whether two rival powers might find common ground — or simply trade advantages — on Middle East stability hung quietly over the tarmac. History reminds us that the grandest gestures of