Ramon Casha states that Josephus, the first century Judeo-Roman historian, refers to the existence of Jesus only as someone worshipped by a new group known as Christians.

In book 20, chapter 9, verse 1 of his Antiquities, Joesphus makes specific reference to “Jesus, known as the Christ”.

I think that counts as pretty good evidence of His existence.

His dismissal of the gospels as evidence of Jesus’ existence purely on the basis of the fact that they were written “decades” later, similarly does not hold water. Jewish scholars often transmitted factual information verbally, so the absence of strictly contemporary account of the life of an itinerant teacher, even one of the stature of Jesus, does not suggest inaccuracy.

Simple logic should inform Mr Casha that it is extraordinarily unlikely that the Apostles (who were all first hand witnesses to His ministry) would have been so remarkably successful in spreading the Word, and been willing to submit to deprivation, torture and quite grisly deaths, had there been no substance to their beliefs.