More than a year after national security officials revealed that Chinese hackers had systematically infiltrated U.S. telecommunications networks, the top Senate Democrat on the committee overseeing the industry is calling for hearings with executives from the nation’s biggest telecom companies. In a public letter released Tuesday, Sen. Maria Cantwell, D-Wash., called for the CEOs of Verizon and AT&T to appear before Congress and explain how the hacking group known as Salt Typhoon breached their