Political party strength in U.S. states has seen significant historical shifts, with the Democratic Party dominating the "Solid South" from the late 1870s into the 1960s, while Republican strongholds existed in New England and parts of the Midwest for much of the 20th century. A major realignment occurred from the 1970s to the 1990s, as the Republican Party became dominant in the South, and the Democratic Party gained control in New England and key coastal states.

The 2010 U.S. state legislative elections marked a pivotal moment, with the Republican Party gaining control of 20 additional chambers and securing a majority of legislative seats nationwide. Since this election, Republicans have largely maintained their majority in state legislative chambers and governorships. As of 2024, this results in 23 Republican trifectas (where one party controls the governorship and both legislative chambers) and 17 Democratic trifectas, though Democratic trifectas now collectively represent a majority of the national population. Other metrics, like the Cook Partisan Voting Index and Gallup polling, also track shifts in state-level party preference.