Some ‘key points’ from “The Republicans’ ‘Excess Seat’ Edge in State Legislatures: Republicans punch above their weight compared to presidential results in more places than Democrats” by Louis Jacobson at Sabato’s Crystal Ball:

“We analyzed 48 states to see which have the most lopsided state Senate and state House chambers compared to how the state voted for president.

Both parties have some states in which the legislative breakdown significantly exaggerates the patterns of the presidential vote.

For Democrats, Hawaii, Rhode Island and Massachusetts have the most “excess seats” above the presidential vote threshold. For Republicans, the list is both longer and more varied, with Florida, Ohio, and Wisconsin standing out as at least somewhat competitive states where the Republicans have large excess seat advantages.

In all, Republicans have proven much more adept than Democrats at leveraging presidential vote patterns into even larger majorities in state legislative chambers. The GOP has achieved significant levels of excess seats in about three times as many states as the Democrats have.

Gerrymandering is one reason for this, but it probably doesn’t explain the exaggerated legislative majorities in many states. Rather, the phenomenon of excess seats appears to be a natural consequence of minority parties being doomed into irrelevance once they start consistently losing presidential and statewide races, sapping their ability to recruit candidates and build party infrastructure.”

Jacobson provides a useful hover map of the U.S., which gives the details for each of the 48 states. At quick glance, it appears that Virginia, Oregon, Washington and Michigan have the smallest ‘excess seat’ ratios, which means the D and R percentages of their presidential vote and party distribution in states legislatures are closely aligned.

While gerrymandering accounts for a lot of the dissonance between state legislatures and presidential votes of each of the unaligned states, Jacobson notes, “My guess, though, is that gerrymandering, and even geography, matters less than one might think. I suspect that it has more to do with the minority party turning headlong into a spiral of irrelevance.” Substitute “incompetence” for “irrelevance,” and you have a more useful distinction, which may be corrected, in some cases, with a little house cleaning.