Lobbying is key to US politics, and never more so than during an election year. BBC News Online looks at the key issues that are likely to feature in the coming months and the main interests groups that are certain to play a part.
Click on the headings below to find out about particular issues and groups.
The 'grey lobby':
About 13% of Americans are over 65. They vote in higher numbers than other age groups and are relatively politically undecided.
Pensioners have become a growing political force
The nation's largest organisation representing senior citizens is the American Association of Retired Persons (AARP). With 30 million members, the group does not make party contributions but is rated as one of the most powerful lobby groups in America. The AARP is supposed to be non-partisan but has traditionally leaned towards the Democrats.
One of the key issues concerning senior citizens is Medicare, the government-run medical insurance system for the elderly, and the rising cost of prescription drugs. Medicare provides hospital care but not prescription drugs. Pensioners have become a growing political force, especially in crucial states such as Florida.
Republicans presented the prescription drugs bill enabling Medicare to begin offering optional prescription drug coverage in 2006. AARP backed the move but the Democrats say the measures do not go far enough.
Many commentators predict the issue will dominate the social agenda in this year's elections. But whether it will really sway voters when it comes to November is not clear.
What is certain, however, is that conservative activists will ensure that voters hear a lot about gay marriage.
President George W Bush has already come under enormous pressure from his evangelical Christian supporters. In February, he announced that he wanted to amend the constitution to establish marriage as solely between a man and a woman. This was a change from 2000 when, running for his party's nomination, Mr Bush opposed gay marriage but said individual states could "do what they want".
Gay marriage is expected to dominate the social agenda of this year's elections
Some commentators and Democratic sceptics say that the president's chief political adviser Karl Rove has his eye on four million evangelical Christians he believes voted in 1996 but failed to vote in 2000 because they were not inspired by Mr Bush's campaign. They say Mr Rove is using the gay marriage issue to draw them out.
Mr Bush's move was commended by the Christian Coalition, the largest and most active conservative grassroots political organisation in America. It has some two million members and lobbies Congress and the White House on numerous issues. Another powerful conservative group Focus on the Family has used its nationwide newsletter and radio network to advocate state bans on gay marriage.
There are numerous other smaller grassroots groups. One of these, the Traditional Values Coalition, is sending out a fund-raising letter entitled the Homosexual Alert Fund to half a million households. It hopes to persuade campaign donors to make it clear to legislators that they will withhold money from candidates who do not support a ban on gay marriage.
The Human Rights Campaign is the nation's largest gay political group. It is a grassroots campaign force of over 500,000 individuals and calls for equal rights for same-sex couples.
John Kerry opposes gay marriage but supports civil unions. This would not give gay couples access to the to the benefits married couples receive under 1,138 different federal statutes.
There are 38 million Hispanics in the US. At 13% of the population, they have overtaken African-Americans to become the country's largest minority. Some 21.5 million are registered to vote and 6.7 million of those are expected to do so in November's presidential election.
Republicans and Democrats have made it clear that they plan to court these voters aggressively.
More than 60% of illegal workers in the US are Mexican
In 2000, 90% of black voters cast their ballot in favour of Democratic candidate Al Gore, while only six per cent voted for Mr Bush. On the other hand, only 35% of Hispanic voters voted for Democrats and the vast majority did not vote at all.
A recent opinion poll of Hispanic Americans found that 53% of them saw themselves as politically independent making them one of the biggest swing voting blocks.
There are, for example, millions of Hispanic votes to be had in key states like Florida, New Mexico, Arizona and North Carolina.
Mr Bush recently introduced new proposals on illegal immigration and extended legal status to immigrant workers. This, however, irritated conservative Republicans.
Hispanic voters are increasingly aware of their growing importance. The largest Hispanic lobby group in the country is the National Council of La Raza, which welcomed the proposals, saying any attempt to resolve problems faced by millions of illegal workers was welcome. But it also suggested that Mr Bush's proposal was skewed in favour of employers who would benefit from the surge of cheap labour.
The federation of American unions, AFL-CIO, includes more than 13 million of America's worker is 64 member unions working in virtually every part of the economy. It has thrown its weight behind John Kerry.
According to the Centre for Responsive Politics, organised labour gave $85m to the Democrats during the 2000 election cycle, but the Democrats still lost the White House and, even with another $90m of labour money in 2002, are the minority party on Capitol Hill.
The Center for Responsive Politics says the money labour unions donate to parties is usually just a fraction of the money that business gives.
Ousting George W Bush in November is the top priority of most union groups but some commentators say Mr Bush remains personally popular with many white-male union members. In the 2000 election, union members voted for Democrat Al Gore over Mr Bush by roughly a two-to-one margin.
Millions of Americans continue to support environmental causes, but the Center for Responsive Politics, which monitors donations and special interest activity, says political contributions from environmental groups are but a fraction of those given by the industrial giants they generally oppose.
It says one of the largest lobby groups, the Sierra Club, spends its money on direct "issue ads" rather than donating to candidates or parties. But, it says, it stills lacks the massive spending power of oil companies, power utilities, chemical companies and "the many other industries who tend to be on the opposite side of environmental legislation in Congress".
The League of Conservation Voters is a group of some nine million environmentally concerned voters who pressure government.
Budget and taxes:
The growing US budget deficit is becoming an important political issue in the campaign.
The gap between tax receipts and government spending is expected to reach more than $500bn in 2004, 5% of the total size of the US economy.
Fiscal conservatives in both political parties worry that high budget deficits could ultimately bankrupt the US economy, forcing up interest rates and crowding out private investment.
The Bush administration says that the high deficit is caused by temporary factors, including the costs of fighting the war on terror and large tax cuts that were needed to get the economy out of recession.
And they say they will get it under control by a tight squeeze on non-defence public spending.
But the fiscal conservatives are worried that without major changes in entitlement programmes like Medicare and Social Security (the costs of which will soar in the next decade as more baby boomers retire) the deficit will still spiral out of control.
It is mostly elite groups, such as the Concord Coalition, that lobby policy makers and run ads in the New York Times. The National Taxpayers Union, which wants tax cuts, is active at the grassroots level in the Republican party.
Issue ads and voter mobilisation efforts:
There are a number of relatively new special-interest groups that plan to spend millions of dollars trying to influence the election through issue advertising and voter mobilisation efforts. These are tax-exempt organisations, known as 527s after a clause in the Internal Revenue Code. Although they cannot contribute to candidates, they can take unlimited funds from individuals, companies and labour unions for issue advertising and get-out-the-vote efforts.
These groups have mainly attracted funding from a few wealthy individuals, including international financier George Soros, who has pledged $10m to several groups, and unions who support the Democrats.
America Coming Together, a voter-mobilisation effort led by a former a AFL-CIO union official and the head of the women's political-action committee EMILY's List. The Centre for Responsive Politics says it had raise $30m by January 2004, with a goal of $75 million.
MoveOn.org, which begun in 1998 to protest the impeachment of President Clinton. The group has become a powerful political action committee supporting Democratic candidates. Its Voter Fund is raising money for TV ads in key battleground states that urge the defeat of President Bush. Mr Soros is a big supporter.
The Media Fund is one of the leading groups dedicated to defeating President Bush in November. It plans to raise close to $100m for an issue-ad campaign in key battleground states to support the Democrats.
Thomas Mann, a politics expert at the Brookings Institution says many of the 527 groups are unlikely to meet their financial targets.
Further, the fund-raising activity of such groups is currently being reviewed by the Federal Election Commission.