  Warm, large exoplanets with 10-100 day orbital periods pose a major challenge
to our understanding of how planetary systems form and evolve. Although high
eccentricity tidal migration has been invoked to explain their proximity to
their host stars, a handful reside in or near orbital resonance with nearby
planets, suggesting a gentler history of in situ formation or disk migration.
Here we confirm and characterize a pair of warm, large exoplanets discovered by
the TESS Mission orbiting K-dwarf TOI-216. Our analysis includes additional
transits and transit exclusion windows observed via ground-based follow-up. We
find two families of solutions, one corresponding to a sub-Saturn-mass planet
accompanied by a Neptune-mass planet and the other to a Jupiter in resonance
with a sub-Saturn-mass planet. We prefer the second solution based on the
orbital period ratio, the planet radii, the lower free eccentricities, and
libration of the 2:1 resonant argument, but cannot rule out the first. The free
eccentricities and mutual inclination are compatible with stirring by other,
undetected planets in the system, particularly for the second solution. We
discuss prospects for better constraints on the planets' properties and orbits
through follow-up, including transits observed from the ground.
