This is the second in a pair of works which study small disturbances to the plane, periodic 3D Couette flow in the incompressible Navier-Stokes equations at high Reynolds number Re. In this work, we show that there is constant
0
>
c
0
≪
1
0 > c_0 \ll 1
, independent of
R
e
\mathbf {Re}
, such that sufficiently regular disturbances of size
ϵ
≲
R
e
−
2
/
3
−
δ
\epsilon \lesssim \mathbf {Re}^{-2/3-\delta }
for any
δ
>
0
\delta > 0
exist at least until
t
=
c
0
ϵ
−
1
t = c_0\epsilon ^{-1}
and in general evolve to be
O
(
c
0
)
O(c_0)
due to the lift-up effect. Further, after times
t
≳
R
e
1
/
3
t \gtrsim \mathbf {Re}^{1/3}
, the streamwise dependence of the solution is rapidly diminished by a mixing-enhanced dissipation effect and the solution is attracted back to the class of “2.5 dimensional” streamwise-independent solutions (sometimes referred to as “streaks”). The largest of these streaks are expected to eventually undergo a secondary instability at
t
≈
ϵ
−
1
t \approx \epsilon ^{-1}
. Hence, our work strongly suggests, for all (sufficiently regular) initial data, the genericity of the “lift-up effect
⇒
\Rightarrow
streak growth
⇒
\Rightarrow
streak breakdown” scenario for turbulent transition of the 3D Couette flow near the threshold of stability forwarded in the applied mathematics and physics literature.