Voting rules and the two-party system
Most US elections use single-member districts with plurality rule: the candidate with the most votes wins, even without a majority. Political scientists note that such systems tend to produce two major parties, a pattern called Duverger's law: voters avoid "wasting" a vote on a likely loser. Other democracies often use proportional representation, which gives seats in proportion to votes and supports more parties.
For president, voters choose electors in each state. In 48 states and DC the candidate with the most votes in the state receives all its electoral votes (winner-take-all); Maine and Nebraska split theirs. A candidate needs 270 of 538.
Primaries and general elections
Parties choose nominees by primaries (voters choose) and caucuses (party members meet and choose). Rules differ by state and party: in a closed primary, only registered party members vote, while an open primary lets other voters take part. Congress has regular elections every two years; the president is elected every four years and one-third of senators every two years. Midterm elections are those held halfway through a president's term.
Parties and interest groups
Parties recruit candidates, organise campaigns and organise Congress. Interest groups try to influence policy without running candidates. They lobby officials, mobilise members, file court briefs and support campaigns. Political action committees (PACs) raise and spend money in elections, subject to rules set by law and court decisions. Campaign finance is a policy area where scholars and citizens disagree about how to balance free speech against concerns about influence.
Public opinion and polls
Political socialisation (through family, school, peers, media) shapes attitudes. Polls estimate public opinion from a sample. A well-designed random poll has a margin of error of roughly 1 ÷ √n.
Worked example: reading a poll
A random poll of 1,000 adults finds that 54 percent support a proposal.
- Margin of error is about 1 ÷ √1000 = 1 ÷ 31.6 ≈ 3.2 percentage points.
- So support is likely between about 51 and 57 percent. Since the range is above 50 percent, a majority likely supports it, though the margin is fairly close.
- If support were 51 percent, the range would be about 48 to 54 percent, and the poll could not tell us whether a majority supports it.
- A poll of 4,000 adults would cut the margin to about 1.6 points.
Question wording, order and sampling methods can bias polls even when the margin of error is small.
The policy cycle
Public policy typically moves through stages: agenda setting (an issue gets attention), formulation (options are developed), adoption (a law or rule is enacted), implementation (agencies and state governments carry it out) and evaluation (results are assessed, leading to change or repeal). Policy is made at several levels at the same time, and many actors can block change, which is why it often moves incrementally.
Turnout
Voter turnout tends to be higher in presidential than in midterm years, and higher among older, more educated and higher-income citizens. Registration rules and the day and time of elections affect participation.