Few Iowa politics watchers doubt that Democrats will gain ground in the state House today–the only question is how much will the Republican majority shrink.

In contrast, the Iowa Senate landscape could shift in either direction. Republicans now hold 29 seats and are unopposed in Senate district 1, where independent Senator David Johnson is retiring. They are also outspending several Democratic incumbents in districts Donald Trump carried in the last presidential election. Democrats currently hold 20 Senate seats, but they could add to their ranks today, despite a difficult map and a couple of bad breaks over the summer.

Here’s how the key races look going into election day, based on voter registration totals, recent voting history, absentee ballot numbers, and where Democratic or Republican leaders have made large expenditures.