In mid-term elections which could hinge on turnout, both Republican and Democratic parties have been doing all they can to get their voters to the polls.
A key weapon in the fight for turnout is the ballot proposition: a local initiative attached to the vote which will galvanise electors on ideological or social grounds.
The strategy was used to effect in the 2004 presidential elections, when emotionally-charged issues like same-sex marriage helped sway voters.
This year's mid-term polls - where local issues play big - will see attempts once again to capitalise on the power of the proposition, especially in swing states.
STEM CELL RESEARCH
In Missouri - where the Democrats have identified one of the six potentially winnable seats they need to take control of the Senate - a ballot initiative to allow stem cell research has become a defining issue.
Fox has endorsed Democrats who back stem cell research
Polls put Democratic challenger Claire McCaskill, in the "yes" camp, and the incumbent Republican Senator Jim Talent neck-and-neck.
Actor Michael J Fox, who has Parkinson's Disease and supports stem cell research, has stepped into the fray with a high-profile campaign advert in which he backs Ms McCaskill.
Sen Talent must keep the support of conservatives who are opposed to the research, without going so far that he alienates undecided moderate voters.
In Maryland, candidates for the open Senate seat have based their campaigns around the debate on stem cell research, although no referendum is on the ballot.
Democrats in governorship races in Wisconsin, Maine and Massachusetts are also trying to use the issue against the Republicans. President George W Bush is opposed to the research.
Voters in eight states - Colorado, Idaho, Pennsylvania, South Carolina, South Dakota, Tennessee, Virginia and Wisconsin - will be balloted on proposals to ban same-sex marriage.
A New Jersey ruling has reignited the debate over same-sex marriage
The Republicans will hope to bring religious conservatives, their traditional support base, flocking to the polls to back any ban. Democrats will seek to dynamise their supporters to oppose it.
A ruling in New Jersey giving gay couples the same rights as heterosexual couples has worked to reignite the debate - probably to the Republicans' advantage. President Bush was quick to make use of the issue in a stump speech in Iowa.
In Virginia, an increase in conservative turnout could help Republican Senator George Allen, whose re-election campaign was hit in the summer by controversy over an alleged racial slur.
In Wisconsin, Republican Mark Green - who supports a ban - may see the benefit as he seeks to beat Democratic Governor Jim Doyle at the polls.
Measures to raise the minimum wage may lend a hand to the Democrats in half-a-dozen tight races for Senate or governorships.
Voters in Arizona, Colorado, Missouri, Montana, Ohio and Nevada will be balloted on whether to raise wages from the federal minimum of $5.15 (£2.70) an hour.
While less emotive than some propositions, polls suggest minimum wage measures are popular and so will increase turnout, to the advantage of the Democrats.
The party is hoping to capitalise on concerns over the state of the American economy, which may be slowing down after a long period of growth. US voters also felt the pinch of higher gas prices earlier this year.
The abortion issue will be galvanising voters in South Dakota.
South Dakota will vote in a referendum on a strict abortion ban
Earlier this year, the state legislature passed a law under which all abortions are banned - including in cases of rape or incest - unless the mother's life is at risk.
However, pro-choice campaigners gathered enough signatures to put a referendum on the ballot, giving voters the option to repeal the ban - or back it.
Supporters of the law, one of the toughest in the US, hope the case could help challenge the 1973 Roe v Wade US Supreme Court decision that legalised abortions everywhere in the country.
However, the issue is creating divisions even within the state's anti-abortion camp, with some believing the measures - signed into law by Republican Governor Mike Rounds - are too restrictive.
Michigan is to vote on a ballot initiative to ban affirmative action which, if approved, would bar public institutions from considering race, ethnicity or gender in public employment and education.
Supporters of Proposition 2 say civic society should be entirely equal, with race or gender playing no part in such processes as university admissions.
However, the initiative has drawn opposition from many business, academic and civic leaders who fear ending affirmative action policies will be a serious setback for ethnic minorities and women.
Citing the example of California, which passed a similar measure 10 years ago, they argue it could result in court challenges to programmes designed to encourage girls into science and engineering, for example, and prevent employers from recruiting a more diverse workforce.
Polls conducted in October showed voters more or less evenly split on the issue.
Half-a-dozen states have anti-smoking measures on the ballot on 7 November.
Tobacco firms have spent millions on ballot initiative campaigns
In the key swing state of Ohio, voters will be presented with two options.
The first - backed by tobacco-industry money - would impose a partial ban on smoking indoors. The second, backed by anti-smoking groups, would be a more sweeping ban.
Voters in Arizona and Nevada will also find two propositions on the ballot, one stricter than the other, banning smoking in most public places.
A proposition in California would quadruple state cigarette taxes, with the extra revenue going to fund health initiatives and anti-smoking campaigns.
Voters in Arizona, Missouri and South Dakota will also decide on measures to raise taxes on tobacco, though by a lesser degree.
The environmental debate has made it onto the ballot in California, with a proposal to fund alternative energy projects by levying a tax on oil production in the state.
The No on 87 campaign is partly funded by US oil producers
Reports suggest more than $100m (£52.7m) has been spent on the rival campaigns over Proposition 87.
The star-studded, Democrat-backed Yes on 87 camp includes former President Bill Clinton, actress Julia Roberts, tycoon Richard Branson and Google co-founder Larry Page, with the bulk of campaign funding coming from Hollywood producer Steve Bing.
The No on 87 camp is funded largely by "Big Oil", including Chevron and Exxon. Adverts warning voters the measure could hit them at the petrol pump seem to be proving effective.
In addition, Republican Governor Arnold Schwarzenegger - a No campaign supporter - is currently well ahead of Democratic challenger Phil Angelides in the polls.
PRIVATE PROPERTY SEIZURE
States including California, Florida, Georgia, Idaho, Michigan and New Hampshire have ballot initiatives aimed at restricting eminent domain, or the government's power to seize private property.
The propositions are largely a response to a US Supreme Court ruling in 2005 that gave the government the right to seize homes for "public benefit", where previously they could only be taken for "public use".
Many fear the ruling means land can now be requisitioned for commercial ventures that benefit the local economy, not just public projects like road building.
Earlier this year, activists in New Hampshire tried to seize the home of Justice David Souter, who ruled with the majority in the Supreme Court decision, to highlight opposition to it.