Both parties will also be tested in California and Florida, where ballot measures have set new ground rules for redistricting that could provide direction for the rest of the country.
Californians passed a proposition last year that would put redistricting efforts in the hands of an independent bipartisan commission formed solely for the purpose of drawing congressional district lines. The commission is the first of its kind in the country, although it has already garnered its share of controversy for not being non-partisan.
In Florida, voters passed a constitutional amendment that keeps the power to draw district lines in the hands of the state legislature but sets a specific criteria that says boundaries that are drawn cannot favor any political candidate or party. Florida will gain two House seats because of population gains, and although the increase would've favored Republicans, the new law might dent that advantage.