  A nova eruption irradiates and heats the donor star in a cataclysmic variable
to high temperatures $T_{\rm irr}$, causing its outer layers to expand and
overflow the Roche lobe. We calculate the donor's heating and expansion both
analytically and numerically, under the assumption of spherical symmetry, and
find that irradiation drives enhanced mass transfer from the donor at a rate
$\dot{m}\propto T_{\rm irr}^{5/3}$, which reaches $\dot{m}\sim 10^{-6}\textrm{
M}_\odot\textrm{ yr}^{-1}$ at the peak of the eruption - about a thousand times
faster than during quiescence. As the nova subsides and the white dwarf cools
down, $\dot{m}$ drops to lower values. We find that under certain
circumstances, the decline halts and the mass transfer persists at a
self-sustaining rate of $\dot{m}\sim 10^{-7}\textrm{ M}_\odot\textrm{ yr}^{-1}$
for up to $\sim 10^3$ yr after the eruption. At this rate, irradiation by the
white dwarf's accretion luminosity is sufficient to drive the mass transfer on
its own. The self-sustaining rate is close to the white dwarf's stable burning
limit, such that this bootstrapping mechanism can simultaneously explain two
classes of puzzling binary systems: recurrent novae with orbital periods
$\approx 2$ h (T Pyxidis and IM Normae) and long-lived supersoft X-ray sources
with periods $\approx 4$ h (RX J0537.7-7034 and 1E 0035.4-7230). Whether or not
a system reaches the self-sustaining state is sensitive to the donor's
chromosphere structure, as well as to the orbital period change during nova
eruptions.
