In an election for US Representative from California’s 20th Congressional District today, 10/25/10, Republican challenger Andy Vidak is atop incumbent Democrat Jim Costa, 52% to 42%, according to SurveyUSA polling conducted in English and in Spanish for KFSN-TV Fresno.

Costa has experienced across-the-board erosion since SurveyUSA’s last poll 6 weeks ago: Among women, Costa had led by 14, now leads by 2. Among voters age 50+, Costa had led by 3, now trails by 14. Among voters without a college degree, Cost had led by 6, now trails by 11.

Whites vote Republican. Hispanics vote Democrat. If Hispanic turnout is higher than the 36% shown here, Costa performs better, but still trails. For example, if Hispanic turnout is modeled at 40%, Vidak today would lead by 7 points. If Hispanic turnout is modeled at 30%, Vidak would lead by 12 points.

Costa won a 3rd term in 2008 with 74% of the vote. Significant spending by outside groups is occurring in the district, the Fresno Bee reported on 10/23/10. The impact of ads attacking the Democrat, taken out by 2 conservative groups, appears to be reflected in these poll results. It is unclear whether the impact of subsequent ads taken out by national Democrats, which may not yet be reflected in this data gathered 10/21/10 through 10/24/10, can turn the contest around for Costa. Costa trails narrowly among the group of respondents who tell SurveyUSA they have already returned a ballot. Costa would need to materially outperform Vidak among those who have not yet returned a ballot to hold his seat in a year when many incumbent Democrats will lose theirs.