Looking at the recent Hartlepool election results, it does indicate that the candidate chosen was the wrong choice, if the Tories take most of the Brexit/UKIP votes. Labour won a lot of those voters back in 2017, offering a softer Brexit than the Tories, but a Brexit nonetheless. That was Labour's best result in the constituency since 2001. I think Labour thought this would be a safe seat without Corbyn, and dropped in a party favourite, where as it should have been a local candidate from the beginning. They have thrown everything at it since, but it was probably too late by the time they realised they were in big trouble. As well as him being a big remainer, he's also got links to the Saudis and had previously supported NHS cuts when he was an MP in the past.