Most of the states in the United States (about 75%) have a state legislature that has been gerrymandered to favor either the Republican Party or the Democratic Party.

Gerrymandering is the drawing of state legislative district lines in such a way that a political party elects more state legislators than it would ordinarily be entitled to. Gerrymandering creates large numbers of “safe seats” for the dominant party in a state legislature that cannot be lost no matter how voters vote.

But there is a distinct partisan bias to the gerrymandering of state legislatures in the United States. Roughly twice as many state legislatures are gerrymandered to favor the Republicans than are gerrymandered to favor the Democrats.

Those are the results of a 48-state study of gerrymandering conducted by the Center for Politics at the University of Virginia. Louis Jacobson was the lead commentator on the study.

The researchers at the University of Virginia started with the results of the 2020 presidential election between Democrat Joseph Biden and Republican Donald Trump. They assumed the two-party election results in a presidential election were the best measure of party popularity in a particular state.

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In states won by President Biden, the University of Virginia researchers then calculated the Democratic percentage of seats in the state House of Representatives elected in 2022. The Democratic presidential percentage (Biden) was then subtracted from the Democratic percentage of seats in the state House of Representatives. The result was the percentage “excess seat edge” for the Democrats in the state House of Representatives.

The process was then repeated for Democrats in the state Senate. After that, the entire process was repeated for states won by Donald Trump in 2020 and gerrymandered to favor the Republicans.

For example, let’s look at the Republican Party in the state Senate in the typical midwestern state of Ohio. In 2020 Donald Trump won Ohio with only 54% of the vote, but the Republicans swept 79% of the state Senate seats in 2022, thanks to gerrymandering. That gives Ohio Republicans an excess-seat edge of 25% in the Ohio state Senate (79-to-54) and puts the Democrats at a great disadvantage.

The 48-state study did not include Nebraska, which has a nonpartisan unicameral state legislature. It also excluded Alaska, where cross-party leadership alignments reduce party influence.

The University of Virginia researchers grouped Colorado with the small number of states that voted for Joe Biden and whose state legislatures had large Democratic Party majorities. The list included the states of Rhode Island, Hawaii, Massachusetts, Nevada, New Mexico, California, Illinois, Vermont and Maryland.

The most significant result of this study was that about twice as many Republican states (25) than Democratic states (11) strongly exaggerated their presidential votes in their state legislatures. These states with heavily gerrymandered Republican state legislatures included Florida, Wisconsin, Tennessee, Alabama, Missouri, Kansas, Ohio, Georgia, North Carolina and 16 more.

The University of Virginia researchers expressed concern regarding the impact of excess seats, both Democratic and Republican, in American state legislatures. In those cases where a political party gains a significant advantage through excess seats, there is a tendency to go further than public opinion in the state where passing laws is concerned,

In Democratic state legislatures, the state legislature risks becoming much more liberal than the voters. The University of Virginia researchers noted excess seats create “legislative majorities that are more extreme than the voters.”

The researchers argued further that excess seats in Republican-dominated state legislatures in the south have permitted those states to pass strong anti-abortion laws despite public opinion polls showing most voters in those states favor abortion.

Another problem is powerful “excess” majorities in a state legislative chamber will be “riven by ideological factions.” Arguments that used to take place between the two political parties are debated and decided in the majority party, thereby threatening party unity.

But the worst effects of “excess-seat edge,” according to the University of Virginia, are on the minority parties in the state legislatures that fail to gain excess seats and drop into permanent positions of unimportance. They lose the ability to recruit strong candidates for the state legislature and can no longer build a strong political party infrastructure.

One might think a state legislature gerrymandered to unfairly favor one political party over the other is a rarity, but the researchers at the University of Virginia revealed gerrymandering the state legislature for political advantage is a widespread practice among the American states.

It is also notable the Republicans have succeeded in gerrymandering about twice as many state legislatures in their favor as have the Democrats. The inevitable conclusion is these 25-or-so gerrymandered-Republican state legislatures are conservative strongholds spread across the nation.

Tom Cronin and Bob Loevy are news columnists who write about Colorado and national politics.