With a Cook Partisan Voting Index rating of D+36, it is the most Democratic district in Washington.

[2] The 7th is the most Democratic district in the Pacific Northwest, and the most Democratic district on the West Coast outside the San Francisco Bay Area or Los Angeles.

Democrats dominate every level of government, and routinely win elections with well over 80% of the vote in this district.

Washington's seventh seat in the U.S. House was added after the 1950 census, but the state did not immediately reapportion.

Democrat Donald H. Magnuson won all three at-large elections.