  It is claimed by a recent quantum Monte Carlo simulation that the
linear-in-temperature DC resistivity observed in the high-$T_{c}$ cuprate
superconductors can be reproduced in the pure two dimensional Hubbard
model\cite{Huang}. Here we show perturbatively that such a translational
invariant electronic model can not support a steady state current in the
presence of a uniform electric field at any finite temperature. Instead, the
Hubbard model is perfectly conducting in the linear response regime and will
undergo Bloch oscillation at finite electric field for any finite temperature.
Nevertheless, the quantum Monte Carlo simulation can provide us the key
information on the temperature dependence of the Drude weight, a quantity of
central importance in the holographic description of the transport properties
of the strange metal phase.
