Historians have standards for establishing historicity. Lincoln meets those standards; Jesus doesn't. The End.

This does not mean of course that a particular person named Jesus of Nazareth didn't exist, however embellished the accounts of his life may have been -- or that he didn't found Christianity. It simply means there's no convincing evidence that he did. (Yes, I'm a mythicist, not a traditionalist in this regard). There's also a fair bit of evidence that he did NOT ... always assuming of course that a person is willing to entertain it to begin with.

In any event atheism has nothing to do with whether Jesus is a historical figure or not, it has to do with whether supernatural beings and realms are falsifiable, enabling one to make knowledge claims about them, which creates the potential for affording belief to them. It is a total deflection.