During the last week before the filing deadline, Republican State Senators Mark Chelgren and Rick Bertrand announced that they will not seek re-election in 2018. Iowa Senate districts 41 and 7 were already the best Democratic pickup opportunities on a difficult midterm election map. Of the 29 Republicans now serving in the upper chamber, only four–Chelgren, Bertrand, Dan Dawson, and Tom Greene–hold seats where registered Democrats outnumber Republicans (barely in Dawson’s district). Dawson and Greene won’t be up for re-election until 2020.

Winning an open seat is usually easier than defeating a legislative incumbent, and Bertrand’s retirement clearly improves Democratic chances in Senate district 7.

But Republicans have likely increased their odds of holding Senate district 41 by swapping out Chelgren for Mariannette Miller-Meeks.