The story behind it is that he was finally shown how terrible his numbers really were in swing states. Apparently, they looked very bad and were trending even further down.

The story also goes that the reality of the situation had largely been hidden from him by his closest confidants up to that point. Add in all the party and public pressure, and it really doesn’t seem too far fetched that he was finally forced to face up to the bleak outlook of his chances going forward.