Twenty years ago, a DNA test (a cheek swabbing) was enough to determine the respondent's ancestral island or continent—or even narrower than that. Back then, the test cost less than $200. In Danney's case, it would narrow down the possibilities.
I hope Danney has had his own Danney tested. While, non definitive, there is some process of elimination in terms of the revealing ancestry. Suppose the DNA came back as 1/2 Caucasian, and specifically Italian, Greek, Portuguese, or Slavic. well then, that would eliminate Bill. (This is assuming Bill’s ancestry is well defined.)
Likewise with Danney’s blood type. If Bill Clinton’s is a known type (0-) and Danney’s momma’s is AB, there are certain genetic absolute blood types that would occur from in their resulting offspring.