Looks like I'm behind the times. I checked his wikipedia page because I remembered he ran for Governor of Kentucky, but the page didn't list his political affiliation in that race. But in 2019, he ran for State Auditor as a Democrat. So perhaps he isn't!
In the grand scheme of things, both major US partys still primary subscribe to some version of liberalism at their core, although that's changing on both fronts.
People need to realize that in a world wide perspective, liberals are considered right wing for being capitalist. They're only left wing in the fucked up US political landscape that is so far skewed right.