Honestly I'm not even sure why Republicans are so invested in flipping KY. Beshear has little actual power as all his vetoes can easily be overridden. He's basically a popular figurehead for the state, like some kind of constitutional monarch or ceremonial head of state. Just leaving him be would be for the best for the state, as it gives us stability and someone Democrats can point to with pride while Republicans can still implement all their policies.
Probably the real reason is to set up Cameron to be McConnell's successor. But I was honestly surprised he ran, as I thought it was an unnecessary risk for him; Cocaine Mitch is probably retiring soon, and Cameron could have been next in line as AG without risking a humiliating defeat in this race. Maybe a secondary motivation is to eliminate Beshear as a threat for a future spot on a Democratic presidential ticket as a popular governor of a red state, and perhaps there's even an element of revenge motivating them. After all, Trump said he'd be the biggest loser ever if Bevin lost. Still, if I were them, I'd just have thrown up a sacrificial lamb candidate and not cared much if Beshear won. The GOP might be getting greedy here; if Cameron loses, which now looks likelier than not, he'll be tainted and less likely to win a primary to be McConnell's successor.
Even with a loss here, I think Cameron would still be the front-runner in a primary to succeed McConnell in 2026. He's the kind of candidate the NRSC would probably try to clear a primary field for (African-American, recent statewide officeholder).