  The standard paradigm of collisionless cold dark matter is in tension with
measurements on large scales. In particular, the best fit values of the Hubble
rate $H_0$ and the matter density perturbation $\sigma_8$ inferred from the
cosmic microwave background seem inconsistent with the results from direct
measurements. We show that both problems can be solved in a framework in which
dark matter consists of two distinct components, a dominant component and a
subdominant component. The primary component is cold and collisionless. The
secondary component is also cold, but interacts strongly with dark radiation,
which itself forms a tightly coupled fluid. The growth of density perturbations
in the subdominant component is inhibited by dark acoustic oscillations due to
its coupling to the dark radiation, solving the $\sigma_8$ problem, while the
presence of tightly coupled dark radiation ameliorates the $H_0$ problem. The
subdominant component of dark matter and dark radiation continue to remain in
thermal equilibrium until late times, inhibiting the formation of a dark disk.
We present an example of a simple model that naturally realizes this scenario
in which both constituents of dark matter are thermal WIMPs. Our scenario can
be tested by future stage-IV experiments designed to probe the CMB and large
scale structure.
