My guess is that Democrats are going to waste a lot of time attacking Vance as an extremist and bringing up his sometimes over-the-top Never-Trump-era attacks on the man he’s now serving as running mate.
The quotation strategy won’t work because Vance can just say he changed his mind about Trump, as a lot of people have. The extremism strategy won’t work because voters rarely care about the ideological positioning of a veep nominee. But at the moment the Democrats are floundering, so strategies that are easy to devise and implement will be attractive.