The GOP hate machine will do this to whoever the opponent is. With the same force and fervor.
When it's someone like Biden, it becomes, "The enemy is terrified. Good."
Certainly the longer he fights Biden, the more invested he is in those lines of attack.
But the hate machine is a munitions factory.
If Sanders wins, they will seamlessly pick up entire lines of attack, pivot their aim to the left, and continue fire without missing a beat.
"Why did Bernie Sanders never call for Hunter Biden to testify?"
"Biden was the frontrunner. What did Bernie [have on/give to] the famously corrupt Biden to get him to throw the election?"
It's about GOP strategy and reading the wrong lessons off from it.