October. Even though the curruption charges are completely bogus, the mere talk of it will hurt him. He might able to overcome it again (although I doubt it), but I think polling over the next couple of weeks will be bad for him.
I don't think these charges are going to affect Biden's numbers. If anything they will cause sympathy as he will be seen as the victim of another Trump/Republican conspiracy.
Yeah. I'm far from a Biden supporter, but I'm a bit puzzled about how everyone is acting like it's a given that the whole Ukraine thing is going to destroy his campaign. I mean, I guess it could happen, but I don't think that's a certainty.
Then think of it this way:
1) Biden is the frontrunner mostly because he is deemed the candidate best equipped to beat Trump, which is what most democrats care the most about currently.
2) Hillary Clinton lost in 2016 because of (bogus) claims that she was corrupt.
If you agree with the above two points, then it isn't hard to see why (bogus) corruption charges against Biden makes him look very vulnerable in an election against Trump and hence makes Biden no longer appear as the most electable of the democrats, in which case the strongest argument for supporting Biden crumbles.