Member's of Congress are supposed to vote the "at home population's desires". Unfortunately, this has been tainted and hard to determine with the Special Interest Groups and Political Action Committees. Some, vote for what would make them money, at least for re-election contributions. Others trade votes, so they can get a piece of legislation that they have written passed. There is a vast number of things that could influence the vote on any one topic.
Party Labels is the most powerful predictor in a congressional voting.
health
Party Identification
Voting is the most powerful act of political participation
Voting on a bill
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intention, influenced by the belief that on'es friends were doing it
Constituency influence.
AARP
If participation is intended to solve a problem, then its major predictor is the obtention of the goal for which it was intended.
1790's
The Congress of the United States.