It was once billed as a model of socialist fraternity: South America's first high-speed train, powered by Chinese technology, crisscrossing Venezuela to bring development to its backwater plains. Now all but abandoned, it has become a symbol of economic collapse — and a strategic relationship gone adrift. Where dozens of modern buildings once stood, cattle now graze on grass growing amid the rubble of the project's gutted and vandalized factory. A red arched sign in Chinese and Spanish is all that remains of what until 16 months ago was a bustling complex of 800 workers. That's when the project's Chinese...