I don't think Corbyn's necessarily an idiot: he's a solid campaigner for example who knows how to connect with voters without seeming like an utter weirdo, and that's often shown itself when he can be arsed, but at the same time I don't think he's a particularly brilliant strategist or a political mastermind. And I think a lot of his weaknesses inevitably show through when he's dealing with an issue that's undoubtedly important to the country, but which doesn't grab his own personal interest. Brexit qualifies in that regard: it's the biggest issue Britain's faced in generations, but Corbyn's not passionate enough for either side to have all that much of a stance on it. Hence he's fluctuated from position to position, with no real coherent strategy beyond what might be good electorally, the same style of politics his supporters lambasted Labour leaders for.