  We consider the bremsstrahlung energy loss of high energy partons moving in
the quark-gluon plasma, at weak coupling. We show that the rates for these
processes receive large O(g) corrections from classical (nonabelian) plasma
physics effects, which are calculated. In the high-energy (deep LPM) regime
these corrections can be absorbed in a change of the transverse momentum
broadening coefficient $\hat{q}$, which we give to the next-to-leading order.
The correction is large even at relatively weak couplings $\alpha_s\sim 0.1$,
as is typically found for such effects, signaling difficulties with the
perturbative expansion. Our approach is based on an effective
"Euclideanization" property of classical physics near the light-cone, which
allows an effective theory approach based on dimensional reduction and suggests
a new possibility for the nonperturbative lattice study of these effects.
