iPoll
The largest archives of public opinion polls with over 500,000 questions and answers asked in the U.S. since 1935.
ICPSR
Inter-university Consortium for Political and Social Research (ICPSR) is a membership-based, not-for-profit organization serving member colleges and universities by providing access to a large database of machine-readable social science data sets.
Roper Polling
Mostly US polling data beginning in the 1930s.
American Political Parties and Elections by 
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