Ehrman himself admits there are no contemporary eyewitness accounts, no archaeological remains, and no Roman records of Jesus. Doesn’t that undercut the confidence?

Ehrman does say that, and then explains why it changes nothing: almost no one from the ancient world outside the ruling class left that kind of documentation, including plenty of figures whose existence nobody doubts. What survives for Jesus is unusual for a first-century Jewish teacher: several independent written sources within a generation, hostile references from Roman and Jewish writers, and a named brother attested by a non-Christian historian. The absence of a birth certificate or an inscription is the ordinary condition of ancient history, not a special problem for Jesus.