America’s top general on Tuesday vehemently defended his Jan. 8 phone call with Chinese military leaders, telling lawmakers that he was “certain” then-President Donald Trump wouldn’t order an attack on Beijing and wanted to convey that reassuring message to his Chinese counterparts.

Testifying before the Senate Armed Services Committee, Army Gen. Mark A. Milley, chairman of the Joints Chiefs of Staff, pushed back on the narrative that he went around Mr. Trump out of fear the president might order an attack on China during his final days in office.

Some Republicans have called for Gen. Milley’s resignation, accusing him of trying to circumvent civilian leadership of the military by having such discussions.

But Gen. Milley pushed back hard on those attacks.

“I am specifically directed to communicate with the Chinese by Department of Defense guidance,” he said. “These military-to-military communications at the highest level are critical for the security of the United States in order to deconflict military actions, manage crises and prevent war between great powers that are armed with the world’s most dangerous weapons.”