  The angular momentum (AM) evolution of stellar interiors, along with the
resulting rotation rates of stellar remnants, remains poorly understood.
Asteroseismic measurements of red giant stars reveal that their cores rotate
much faster than their surfaces, but much slower than theoretically predicted,
indicating an unidentified source of AM transport operates in their radiative
cores. Motivated by this, we investigate the magnetic Tayler instability and
argue that it saturates when turbulent dissipation of the perturbed magnetic
field energy is equal to magnetic energy generation via winding. This leads to
larger magnetic field amplitudes, more efficient AM transport, and smaller
shears than predicted by the classic Tayler-Spruit dynamo. We provide
prescriptions for the effective AM diffusivity and incorporate them into
numerical stellar models, finding they largely reproduce (1) the nearly rigid
rotation of the Sun and main sequence stars, (2) the core rotation rates of
low-mass red giants during hydrogen shell and helium burning, and (3) the
rotation rates of white dwarfs. We discuss implications for stellar rotational
evolution, internal rotation profiles, rotational mixing, and the spins of
compact objects.
