Whoever decides to step into the breach they will be attacked mercilessly by the media wing of the democrat party.
Just musing here but Donald Trump and family may be the most thoroughly investigated family ever in American politics. That would make Don Trump Jr sort of a pre-screened candidate, making opposition research in him a likely dry hole.
The only way then to smear him would be to make shit up, or maybe set up some phony entrapment play. Either way, it would be more of the same ‘son of orange man bad’. But, by then the public will have been so conditioned by fake news, they’ll ignore the noise as nothing more than partisan politics.
Btw, imagine an articulate Donald Trump. That’s Don Jr.