  Friedel's sum rule provides an explicit expression for a conductance
functional, $\mathcal{G}[n]$, valid for the single impurity Anderson model at
zero temperature. The functional is special because it does not depend on the
interaction strength $U$. As a consequence, the Landauer conductance for the
Kohn-Sham (KS) particles of density functional theory (DFT) coincides with the
true conductance of the interacting system. The argument breaks down at
temperatures above the Kondo scale, near integer filling,
$n_{\text{d}\sigma}\approx 1/2$ for spins $\sigma{=}\uparrow\downarrow$. Here,
the true conductance is strongly suppressed by the Coulomb blockade, while the
KS-conductance still indicates resonant transport. Conclusions of our analysis
are corroborated by DFT studies with numerically exact exchange-correlation
functionals reconstructed from calculations employing the density matrix
renormalization group.
