ok i don't know how KFF is estimating their breakdown by ethnicity, but it looks like they are using total population (all ages) who have received at least one dose.
54% of whites, 46% of blacks, 61% of hispanics, and 75% of asians cannot possibly correlate to the total population rate provided directly by the CDC, which is 73.5%
in the first place, i'm not sure why you want to break it down by ethnicity groups of all ages, when your argument is that less than 90% of registered democrats are vaccinated. afaik children cannot be democrat or republican