IIRC that's basically the plot of "House of Cards". /s
In all seriousness
Depends on if we're talking Mexican style or Russian style assassinations. IMO the only way a bullet goes in the direction of the US president(ial-candidate) is if they want one to.
But a clandestine conspiracy using the full spectrum of technology from auditory weapons, to poisons, to windows... Gets a little dicey.
what's the actual risk of the VP assassinating the president
EoD what is the acceptable % increase in risk? Cuz it's the undeniable increase that's unacceptable from a security perspective.
From a practicality perspective, at what point does mitigating this risk make the entire partnership unproductive and pointless?