Congressional districts are based an equal-sized population for each of them in a given state, the politics comes in with twisting the borders around so you can either muster enough support in a district to get your own guy elected or concentrate all the opposing party's votes into as few districts as possible so your guys end up winning 8 out of 10 seats by 55% and the opposition wins 2 out of 10 seats by 95%. Both parties do it, in fact the Supreme Court in its most Liberal days thought it was just peachy so Black votes could be concentrated enough to elect Black candidates by drawing district boundaries that looked like an amoeba on acid.
In a given year it might be to one party's advantage or the other, it is not something that would ensure a Republican hegemony by any means, it could even hurt them in 2016, but it does redress a lot of the inherent inequities in the current all-or-nothing scheme most states use. After what happened in 2000, you'd think these idiots would be all for it.