Pennsylvania voters handed the U.S. Senate's No. 3 Republican his first political defeat Tuesday, rejecting conservative stalwart Rick Santorum in favor of Democrat Bob Casey, the mild-mannered son of a former two-term governor.

Santorum, a strong voice for conservatives in Washington, had long been a polarizing figure in Democratic-leaning Pennsylvania. Although admired for his blunt talk, he alienated voters with his harsh partisanship and his positions on an array of issues, from support of the Iraq war to his complaint that in too many households both parents work outside the home.

Check Your State, Check Your Race by clicking BALANCE OF POWER dropdown menu above.

• Click here to visit YOU DECIDE 2006, FOXNews.com's complete election center.

Casey's victory was based on a statistical analysis of the vote from voter interviews conducted for The Associated Press by Edison Media Research and Mitofsky International.

A disciplined Casey stuck to his I'm-not-Santorum message throughout his campaign, accusing the Republican senator of pursuing a rigid ideology that put him out of step with Pennsylvanians. A former two-term state auditor and now the state treasurer, Casey was seeking to become the first Democrat from Pennsylvania elected to a full term in the U.S. Senate since 1962.

Unable to gain ground on the front-runner, Santorum mounted ever harsher attacks against his Democratic opponent, in the end accusing him of "aiding and abetting terrorism and genocide" through state pension investments.

Santorum raised $25 million and Casey $15 million, making it the most expensive Senate race in Pennsylvania history.

Check Your State, Check Your Race by clicking BALANCE OF POWER dropdown menu above.

• Click here to visit YOU DECIDE 2006, FOXNews.com's complete election center.