  Recently, the issue of whether the Kondo problem in quantum dots at large
bias is a weak-coupling problem or not has been raised. In this paper, we
revisit this problem by carefully analyzing a corresponding model in the
solvable limit -- the Emery-Kivelson line, where various crossover energy
scales can be easily identified. We then try to extract the scaling behavior of
this problem from various physical correlation functions within the spirit of
``poor man's scaling.'' Our conclusions support some recent suggestions made by
Coleman {\em et al.} [Phys. Rev. Lett. {\bf 86}, 4088 (2001)], which are
obtained by perturbative analysis: The voltage acts as a cutoff of the
renormalization group flow for {\em only} half of the impurity so that the
low-temperature physics is controlled by a strong-coupling fixed point. But the
low-temperature response functions in general show one-channel Kondo behaviors
with two-channel Kondo behaviors occurring only through proximity to a quantum
critical point.
