He doesn't need to explain the whole thing, he just needs to throw the accusation out there in the middle of a foreign policy argument.
"Oh come on Joe, you won't get anything done, not without someone in your family getting a bribe."
"Joe, the whole world knows you're for sale. China, Ukraine, Iran, they just drop some money to Hunter and you let them get away with everything!"
"Joe, you're a sellout, and we've got the paper trail thanks to your screw-up son."
I agree that gun control should be advertised loudly, but I don't know how he works gun control into a debate he's already going to struggle to keep on foreign policy. Ideally, that issue would lead the few ads he's buying right now, but I've seen more Trump ads about Barrett and Biden's gaffes than about actual policy issues.
Incidentally, Barnes did a good breakdown of the laptop issues on Viva Frei's show, connecting a lot of dots and giving the history of the Bidens that is left out of the media narrative.. Most notably, he said he's had personal experience where a client had people
strongly hint that a bribe to the Biden family would help a case go away.