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.

Republicans are all but guaranteed to maintain control of the Iowa Senate after November and could expand their majority, now at 29 out of 50 seats. However, Democrats have a chance to pick up a few districts as they work toward winning back the chamber in 2020.

More Iowa women are running for office in 2018 than ever before, which could lead to record numbers of female state representatives and senators next year.

However, in other meaningful ways, Iowa’s legislature could become less diverse after the November election.

Many Iowa Democrats expect to have the wind at their backs for the 2018 elections, due to surging progressive activism, an unpopular Republican president, and backlash against GOP lawmakers who used their power this year to take rights away from hundreds of thousands of workers, lower wages for tens of thousands more, and undermine protections for those who suffer workplace injuries.

It’s too early to predict the political climate next fall, but Democrats need to hope for favorable external conditions as well as strong recruits and well-run campaigns. New calculations of last year’s presidential election results by state legislative district point to a very steep climb back to 51 seats in the Iowa House and 26 seats in the Senate. This post will survey the terrain in the upper chamber.