  The magnetism and rotation of white dwarf (WD) stars are investigated in
relation to a hydromagnetic dynamo operating in the progenitor during shell
burning phases. The downward pumping of angular momentum in the convective
envelope, in combination with the absorption of a planet or tidal spin-up from
a binary companion, can trigger strong dynamo action near the core-envelope
boundary. Several arguments point to the outer core as the source for a
magnetic field in the WD remnant: the outer third of a $\sim 0.55\,M_\odot$ WD
is processed during the shell burning phase(s) of the progenitor; the escape of
magnetic helicity through the envelope mediates the growth of (compensating)
helicity in the core, as is needed to maintain a stable magnetic field in the
remnant; and the intense radiation flux at the core boundary facilitates
magnetic buoyancy within a relatively thick tachocline layer. The helicity flux
into the growing core is driven by a dynamical imbalance with a
latitude-dependent rotational stress. The magnetic field deposited in an
isolated massive WD is concentrated in an outer shell of mass $\lesssim
0.1\,M_\odot$ and can reach $\sim 10\,$MG. A buried toroidal field experiences
moderate ohmic decay above an age $\sim 0.3$ Gyr, which may lead to growth or
decay of the external magnetic field. The final WD spin period is related to a
critical spin rate below which magnetic activity shuts off, and core and
envelope decouple; it generally sits in the range of hours to days. WD periods
ranging up to a year are possible if the envelope re-expands following a late
thermal pulse.
