republican primary. so the incumbent is not necessarily safe. >> reporter: true, incumbents still aren't safe bumper-to-bumper the threat to them in politically gerrymandered districts full of voters in their own party comes from within, not across the aisle, pulling lawmakers even more to the extreme. chris turner, a democrat. >> there is no scenario in which a republican could win my house district. >> reporter: that could pull you left if you did have a primary opponent. >> sure. there is no question. >> reporter: there are different kinds of gerrymandering. packing, putting like-minded voters together, or cracking, separating them the dilute their influence. after the 2010 census, texas republicans went the cracking route, spreading the democratic vote in austin across republican districts. this time they packed. republican congressman pete sessions' district will be even more red. >> we've by and large entered a period of time where republicans want to be represented by