Biden had no choice but to resign after that debate performance he gave...the world saw what most people already knew and many denied; that he was in extreme mental decline.
The powers that be in the Democrat Party (Obama, Clintons, Pelosi, Soros et al) made him drop out...the day before he was screaming that he was all in to the finish line.
What changed over night?...The Democrats realized that he was almost certain to lose and they will do ANYTHING to stay in power, so he was forced to drop out..There was nothing noble, heroic of patriotic about it...he was coerced into dropping out.
I think the common wisdom is that it was playing dirty ball to deny Obama from the nominating process. As a result we diminished women/family choice and lost support for the Supreme Court. In the end I think it hurt the Republican Party.