Surely punching left will convince leftists that siding with backstabbing liberals will work this time!

I'm likely voting for Biden, for what it's worth, but wouldn't your goals be better served by trying to work with leftists and unalienate them from the electoral process, rather than opting for the shame route? The entire reason why Biden is losing leftist votes is because liberals have been punching left, rather than trying to build a coalition, thus alienating leftist voices.