National redistricting groups are pouring money into the Midwest, where slight changes in state legislative control could help build partisan advantages in the fight to control Congress in the next decade.

A whopping 54 of the Republican State Legislative Committee’s 115 target districts for redistricting lie in Minnesota, Wisconsin, Kansas, Nebraska, and Iowa. Those legislatures hold the keys to redrawing 27 Congressional districts, of which 15 are currently held by Republicans, thanks in part to the party’s redistricting prowess following the 2010 Census.

“The Midwest still matters,” said University of Wisconsin professor Barry Burden.

The Democratic Legislative Campaign Committee said it’s spending a record $16 million on key states—many in the Midwest—in the hope that even small gains can yield a congressional advantage.