Tim Cook faces a tough balancing act between Washington and Beijing to protect Apple's supply chain in China.Justin Sullivan/Getty ImagesFor years, Tim Cook has overseen the development of Apple's supply chain in China.The risk of tariffs on China from Donald Trump requires a complex balancing act from Cook. Jamie MacEwan, an analyst, estimates that "almost half of Apple's revenue is exposed to China."Tim Cook faces an unenviable task this year: keeping a tough-on-China president onside while continuing to lean on the country for Apple's complex supply chain.The Silicon Valley giant has spent years building a vast supply chain network in China under the leadership of Cook, who was first tasked by Steve Jobs in 1997 with devising a cost-cutting outsourcing plan when Apple was on the brink of bankruptcy.From Jiangsu in the east to Sichuan in the west, Foxconn, Luxshare, Pegatron, and others have played pivotal roles in helping Apple generate over $1.8 trillion in net sales this decade alone by serving as the manufacturing conveyor belt for everything from iPhones to Macs.However, Apple's ability to maintain its most important manufacturing network could now depend on how effectively Cook negotiates with President-elect Donald Trump — while appeasing rival powers in Beijing, in whose hands Apple's supply chain largely sits.Trump has signaled a return to the trade war that defined his first term by threatening to slap new tariffs on China.