Probably the only reason he's not DOA is that Republicans are just not willing to concede that Biden is a "well meaning old man".
They're so invested in a crazed, futile, and unending effort to dig up some evidence of corruption that they will forever refuse to let go of this ineffective line of attack and actually capitalize on one that a majority of the American public agree with.
They can't. If they truly present the American public with a choice between a "well-meaning, somewhat befuddled old man" and "fabulist, fraudster, rapist and traitor Donald Trump" they'll lose in a landslide, and lose down-ballot as well. And they know it.