  We show that the short spin-up time observed for the Vela pulsar during the
1988 ``Christmas'' glitch implies that the coupling time of the pulsar core to
its crust is less than $\sim$ 10 seconds. Ekman pumping cannot explain the fast
core-crust coupling and a more effective coupling is necessary. The internal
magnetic field of the Vela pulsar can provide the necessary coupling if the
field threads the core with a magnitude that exceeds $ 10^{13}$ Gauss for a
normal interior and $ 10^{11}$ Gauss for a superconducting interior. These
lower bounds favor the hypothesis that the interior of neutron stars contains
superfluid neutrons and protons and challenge the notion that pulsar magnetic
fields decay over million year time scales or that magnetic flux is expelled
from the core as the star slows.
