Honestly, I disagree with the premise that biden can get into the republican base, let alone the segment within that that makes up trump's base. I mean, what group of republicans can he reliably hope to get? And if those exists, does it make more sense to pander to those than other groups?Of course Trump would mock biden, but for Trump, that would be the smarter move. Biden can get into the republican base to some extent because he is unthreatening (that is why republicans want to claim that he is controlled by 'the left': Because Biden himself is THAT unthreatening).
This is an instance of the campaign playing out Biden's strength while Clinton's campaign failed to play out hers. They wanted to present clinton as something which she was not: A champion for feminism. Clinton is not that person.
But Biden IS a devout catholic, a nice guy and a people person. Putting more emphasis on that by pulling attack ads (but obviously exchanging them for other ads and ramping up your door to door efforts) is a smart move.
Much like it was a smart move not to 'temper trump' when he won in 2016, even tho most people thought he should become 'more presidential' after he won the primary to be able to win.
Ultimately, what does biden have to gain from this? What segment of the republican party can he hope to sway? IMHO this is just barking at tree that conveniently appeared after doing acid. Biden has zero business pandering at any republican. He could maybe win some on account of having the right genitals, unlike hillary, but otherwise is barking at the same imaginary tree as hillary did 4 years ago. Biden should be pandering at groups of people he can win over or maybe convince to vote. Which is younger voters and most importantly undecided independents... Anything further right than that is a lost cause.