  Foreground power dominates the measurements of interferometers that seek a
statistical detection of highly-redshifted HI emission from the Epoch of
Reionization (EoR). The chromaticity of the instrument creates a boundary in
the Fourier transform of frequency (proportional to $k_\parallel$) between
spectrally smooth emission, characteristic of the strong synchrotron foreground
(the "wedge"), and the spectrally structured emission from HI in the EoR (the
"EoR window"). Faraday rotation can inject spectral structure into otherwise
smooth polarized foreground emission, which through instrument effects or
miscalibration could possibly pollute the EoR window. Using data from the HERA
19-element commissioning array, we investigate the polarization response of
this new instrument in the power spectrum domain. We perform a simple
image-based calibration based on the unpolarized diffuse emission of the Global
Sky Model, and show that it achieves qualitative redundancy between the
nominally-redundant baselines of the array and reasonable amplitude accuracy.
We construct power spectra of all fully polarized coherencies in all
pseudo-Stokes parameters. We compare to simulations based on an unpolarized
diffuse sky model and detailed electromagnetic simulations of the dish and
feed, confirming that in Stokes I, the calibration does not add significant
spectral structure beyond the expected level. Further, this calibration is
stable over the 8 days of observations considered. Excess power is seen in the
power spectra of the linear polarization Stokes parameters which is not easily
attributable to leakage via the primary beam, and results from some combination
of residual calibration errors and actual polarized emission. Stokes V is found
to be highly discrepant from the expectation of zero power, strongly pointing
to the need for more accurate polarized calibration.
