93603 leans heavily Republican by roughly 46 points: about 27% of voters vote Democratic and 73% Republican.
About 46% of adults in 93603 typically vote, below the U.S. average of about 62%. Among adults in 93603, ~12% vote Democratic, ~34% Republican, and ~54% don't vote. The map below shows estimated turnout by block group.
How 93603 compares
Among zip codes within 15 miles, 93603 leans more Republican than 5 of 7 neighbors.
93603 runs about 66 points more Republican than California as a whole. California leans Democratic overall, while 93603 is one of the few Republican-leaning pockets.
Politics vary noticeably by block within 93603. The west side is the most Republican-leaning (R+53) and the south side is the least Republican-leaning (R+27), a spread of about 26 points.
Why 93603 leans the way it does
This analysis examined 14,881 data points per zip code to find what predicts political lean and turnout. The items below are a few correlations that stood out for 93603, not a ranked or complete list of what matters most.
93603 votes against the grain of California. California leans Democratic overall, while 93603 runs about 66 points more Republican. Rural areas vote Republican, and 93603 sits in the bottom quarter on density (about 2%, below 97% of zip codes).
Population density, never-married share, and Republican lean
Places that combine low population density and a never-married-heavy adult population tend to lean Republican, as 93603, CA does.
Why turnout in 93603 looks the way it does
Crowded housing lines up with lower turnout. About 8% of homes in 93603 have more than one occupant per room, above 93% of zip codes. Learn more about the findings and methodology on the political spectrum map.
Nearby Zip Codes
Zip Codes with Similar Populations
Sources and methodology
Precinct-level voting records used to fit the model come from California Secretary of State, Elections, distributed by the Voting and Election Science Team. Demographic inputs come from the U.S. Census Bureau (ACS 5-year estimates and the 2020 Decennial Census). Health and environmental inputs come from the CDC (PLACES and the Environmental Justice Index). Land cover comes from the USGS and EPA. Election-day and lead-up weather come from PRISM 4km daily grids and the NOAA Global Historical Climatology Network. Mail-voting and election-administration patterns come from the MIT Election Lab's Survey of the Performance of American Elections. Block-group crime detail comes from CrimeGrade. Internet data and modeling support provided by ISPreports.org.
Modeling and analysis by the BestNeighborhood data science team. Full methodology and findings: political spectrum map.
Methodology reviewed by the BestNeighborhood data team. Last updated May 2026.