  The paper is concerned with a McKean-Vlasov type SDE with drift in
anisotropic Besov spaces with negative regularity and with degenerate diffusion
matrix under the weak H{\"o}rmander condition. The main result is of existence
and uniqueness of a solution in law for the McKean-Vlasov equation, which is
formulated as a suitable martingale problem. All analytical tools needed are
derived in the paper, such as the well-posedness of the Fokker-Planck and
Kolmogorov PDEs with distributional drift, as well as continuity dependence on
the coefficients. The solutions to these PDEs naturally live in anisotropic
Besov spaces, for which we developed suitable analytical inequalities, such as
Schauder estimates.
