Really? I think since the second the campaign has been called he's been almost without flaw.
I went into the election deeply unsure who I would vote for and not convinced by Corbyn, but I think he's done a really good job. They've released a manifesto that appeals to voters, he's been enthusiastic and engaging, he's spoken well to the crowds, he's done well on TV, and they've absolutely hammered the Conservatives as a party for the rich and wealthy. I'm not convinced by Labour's position on Brexit, but they're been less amateur than the Lib Dems on this point.
The only real mistake Labour have made is continuing to allow Diane Abbott to go on TV.