Bush was able to ward off any serious challenge to the Republican nomination. Senator Lincoln Chafee from Rhode Island considered challenging Bush on an anti-war platform in New Hampshire but decided not to run after the capture of Saddam Hussein in December 2003. On March 10, 2004, Bush officially attained the number of delegates needed to be nominated at the 2004 Republican National Convention in New York City. He accepted the nomination on September 2, 2004, and retained Vice President Dick Cheney as his running mate. During the convention and throughout the campaign, Bush focused on two themes: defending America against terrorism and building an ownership society. The ownership society included allowing people to invest some of their Social Security in the stock market, increasing home and stock ownership, and encouraging more people to buy their own health insurance.
The 2004 Democratic Party presidential primaries took place from January 14 to June 8, 2004, to select the Democratic Party's nominee for president. Before the primaries, Vermont governor Howard Dean was a favorite to win the nomination; however, Massachusetts senator John Kerry won victories in two early races: the Iowa caucuses and the New Hampshire primary. These wins strengthened Kerry's previously weak campaign. By March 11, Kerry had received enough delegates to win the nomination. Other major candidates included North Carolina senator John Edwards and retired U.S. Army general Wesley Clark. Kerry asked Republican senator John McCain to be his running mate but McCain turned down his offer. On July 6, Kerry selected Edwards as his running mate, shortly before the 2004 Democratic National Convention was held later that month in Boston.
Heading into the convention, the Kerry–Edwards ticket unveiled its new slogan: a promise to make America "stronger at home and more respected in the world". Kerry made his Vietnam War experience the convention's prominent theme. The keynote address at the convention was delivered by Illinois state senator and U.S. Senate candidate and future president Barack Obama; the speech was well received, and it elevated Obama's status within the Democratic Party.
There were four other presidential tickets on the ballot in a number of states totaling enough electoral votes to have a theoretical possibility of winning a majority in the Electoral College. They were:
• Michael Badnarik / Richard Campagna, Libertarian Party (campaign). Badnarik was nominated on the third ballot and Campagna on the first ballot at the Libertarian National Convention in Atlanta, Georgia, held May 28–31, 2004.
• David Cobb / Pat LaMarche, Green Party (campaign). Cobb was nominated on the second ballot at the 2004 Green National Convention in Milwaukee, Wisconsin, held June 23–28, 2004.

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Ahead of the 2004 election, some states implemented electronic voting systems. Critics raised several issues about voting machines, particularly those made by Diebold Election Systems. Cybersecurity professionals found security vulnerabilities in Diebold machines. Voting machines made by several companies were also criticized for their lack of a paper trail, which would have made results easier to verify. Democrats also criticized various executives at Diebold, Inc. (the parent company of Diebold Election Systems) for their support of Bush's campaign, stating that it constituted a conflict of interest. Following these issues, California banned the use of Diebold's AccuVote TSX voting machines for elections in 2004.
The 2004 election was the first to be affected by the campaign finance reforms mandated by the Bipartisan Campaign Reform Act of 2002. The act created restrictions on fundraising by political parties and candidates. A large number of independent 527 groups were created to bypass these restrictions. Named for a section of the Internal Revenue Code, these groups were able to raise large amounts of money for various political causes as long as they did not coordinate their activities with political campaigns. Examples of 527s include Swift Boat Veterans for Truth, MoveOn.org, the Media Fund, and America Coming Together. These groups were active throughout the campaign season, spending a record $556 million for all elections in 2004.

The Stand by Your Ad provision of the Bipartisan Campaign Reform Act required political advertisements on television to include a verbal disclaimer identifying the organization or campaign responsible for the advertisement. This provision was intended to force campaigns to take responsibility for negative advertisements. Campaign strategists criticized this requirement, stating that it would waste time and cause voters to be confused.

Bush focused his campaign on national security, presenting himself as a decisive leader and contrasted Kerry as a "flip-flopper." This strategy was designed to convey to American voters the idea that Bush could be trusted to be tough on terrorism while Kerry would be "uncertain in the face of danger." In the final months before the election, Kerry's campaign focused on domestic issues such as the economy and health care. Kerry's campaign managers believed that Kerry had an advantage on domestic issues. Bush's campaign also focused on increasing voter turnout among conservatives. According to one exit poll, people who voted for Bush cited the issues of terrorism and traditional values as the most important factors in their decision. Kerry supporters cited the war in Iraq, the economy and jobs, and health care.
Tax cuts were passed in 2001 and 2003 under the Bush administration with Bush's support. Kerry voted against these tax cuts. During the 2004 campaign, Bush praised these tax cuts, stating that they helped to grow the economy. On the other hand, Kerry attacked Bush for failing to create jobs under his presidency. Kerry stated that he wanted to reduce the United States budget deficit by capping government spending while ending various tax breaks for businesses. Kerry also supported tax credits for businesses that hire additional workers. Bush attacked Kerry for his economic proposals, stating that they would cause Americans to pay higher taxes. Bush also attacked Kerry for previously supporting tax raises, such as a proposed increase on the federal gas tax.
Bush defended the Iraq War, arguing that it was necessary to stop terrorism. He also said that the United States had made progress stopping terrorism in other nations. Bush attacked Kerry for opposing the Iraq War after voting to authorize it in 2002, characterizing the shift as one of many flip-flops by Kerry. Kerry argued that Bush had misled the American public in pursuing the Iraq War, noting that no illegal weapons had been found in Iraq. He said that the Iraq War was a mistake and a diversion from terrorism in other nations such as Afghanistan. After the election, exit polls found that foreign policy concerns were the most important issues for voters.
Health savings accounts (HSAs) were introduced in 2004 as part of the Medicare Prescription Drug, Improvement, and Modernization Act, signed by Bush in December 2003. As part of his 2004 campaign, Bush supported the expansion of HSAs. He proposed tax cuts to help Americans purchase their own health insurance. He also proposed a plan that would allow small businesses to purchase health insurance in large groups. Kerry's health care proposals included government subsidies for businesses that provide health insurance and the expansion of government-run health care programs. Health policy experts stated that Bush's proposals would have a more limited impact than Kerry's proposals. Kerry also attacked Bush for his polic…

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