The only poll that showed a huge change over time was Emerson College's; at the beginning of October, Beshear had a 16 point advantage in that poll. At the beginning of November, when Emerson College conducted another poll (right after Trump's endorsement), it had swung to 1 point advantage...for Cameron.
It's easy to interpret the loss as Trump's fault, but at least one piece of polling data does not support that conclusion.
The fact of the matter is, in the long history of Kentucky governors, the vast majority stopped being governors because of (1) term limits; (2) resignation; (3) declining to run for re-election; or (4) dying in office.
The only three governors in Kentucky's history to have lost re-election are:
Democrat James D. Black in 1919 (who had only succeeded a vacancy in the governor's seat, and was not elected into the seat; he only served for five months before losing that year's election)
Republican Ernie Fletcher in 2007 (in a time where there was not only anti-Republican sentiment in the late Bush years, but you had local circumstances of the merit system corruption investigation overshadowing Fletcher's re-election)
Republican Matt Bevin in 2019 (where of the three gubernatorial elections held that year, the Democrats retained Louisiana, and the Republicans retained Mississippi; Kentucky had a humongous turnout compared to the prior 2015 election, with total votes in 2019 exceeding 2015 votes by over 460,000(!); and, more importantly, it was a situation where Matt Bevin's 2018 pension reform bill — heavily criticized by teachers in KY to the point where they actually went on a pseudo-strike — was defeated in the Kentucky Supreme Court by a lawsuit filed by then-Attorney General Andy BeShear, the Democrat who would ultimately defeat him again, except next time it was in the gubernatorial election).
In general, as far as Kentucky gubernatorial elections are concerned: the incumbent always wins.
And, media sentiment notwithstanding (because they're going to be anti-Trump as a matter of course), the data that's available (limited as it is) does not support Trump harming Daniel Cameron's chances.