Across 20 states with completed candidate filing data, 28% of incumbent state legislators are running in contested primaries this year — the second-highest share since 2010, trailing only 2022. At the same time, the share of open seats, at 15.9%, is the second-lowest since 2010.

Among the 20 states with completed 2026 candidate-filing data — Alabama, Arkansas, California, Idaho, Illinois, Indiana, Kentucky, Maryland, Maine, Montana, North Carolina, North Dakota, Nevada, Ohio, Oklahoma, Oregon, South Carolina, Tennessee, Texas, and West Virginia — three patterns emerge compared to those states across even-year cycles since 2010:

Here's a closer look at what's driving the data.

Number of incumbents who are not seeking re-election

Across the 20 states, 15.9% of state legislative seats up for election this year have no incumbent running. That's down from the historical average of 19%, and the second-lowest since 2010. Only 2020 was lower, with 14.7%. Sixteen of the 20 states are below their own historical average for open seats. 

The 20-state set includes 12 Republican trifectas, five Democratic trifectas, and three divided governments — open seats are down across all three categories, with the largest average declines occurring in states with divided governments.

Nevada, which has a divided government, had the largest decline in share of open seats, down 13 percentage points below its historical average. Four states buck the trend and show increases in open seats this year — Maine (+10 points), North Dakota (+7 points), Ohio (+0.5 points), and Texas (+5 points). These trends may change as data from additional Democratic trifectas and divided governments are incorporated compared to the initial large set of Republican trifectas.

Number of incumbents facing primary challengers

Between 2010 and 2024, an average of 24% of incumbents in the 20 states in our analysis had primary challengers. In 2026, 28% of incumbents are running in contested primaries, second only to 2022 at 30%.

Twelve states are above their own historical averages for contested incumbents this year, with the biggest jumps occurring in North Dakota (+22 points from average), Oklahoma (+14 points from average), Oregon (+13 points from average), Indiana (+10 points from average), and West Virginia (+8 points from average).

The overall increase in the percentage of incumbents facing primary challenges would have been larger, except for a decline in Maryland below its historical average. There, incumbents have historically faced the highest average number of challenges among the 20 states we reviewed at 67%.

Maryland remains the state with the highest number of incumbents facing challengers this year, at 51%, 16 points below its average. Had Maryland matched its historical average for incumbent contests, the average across all states would have been nearly one point higher.

Number of primary elections with more than one candidate

This year, an average of 22.8% of possible primaries are contested across the 20 states, 1.3 percentage points higher than the historical average of 21.5%.

While the states are not far from the average number of contested primaries collectively, there are a handful of noteworthy up- and downswings.

Five states are running more than six points above average: Indiana (+10 points), North Dakota (+9 points), Oregon (+7 points), South Carolina (+7 points), and Texas (+6 points). Three states are running more than six points below average: Alabama (-7 points), Nevada (-6 points), and Maryland (-11 points).

Click here to see our analysis of primary election competitiveness in state and federal government this year.