I agree that my original understanding of his definition was incorrect (if anything i was too narrow), but the concept they/I are putting forward still makes the most sense.

Regardless of the percentage of straight GOP voters, there is no good reason why the percentage of voters that like Trump regardless of down ballot choices should be anything other than either the same as or slighty more or less than the straight ticket voters. These are disgruntled/ex- GOPers, first time voters, anti abortion Dems, Bernie Bros, bandwagon riders, etc.