George W. Bush/Al Gore (2000)

The first presidential election on this list is considered the most contentious presidential race in American history, and also one of the closest ones (just days before the election, pollsters said it was too close to call). The presidential election occurred more than two decades ago on December 12, 2000, between George Washington Bush (Republican) and Al Gore (Democratic). George Washington Bush and Al Gore focused on domestic issues, such as the budget, tax relief, and reforms for federal social insurance programs, although foreign policy was not ignored while running for president.

Gore decided not to campaign with Bill Clinton since Clinton had a sex scandal involving Monica Lewinsky. He criticized Bush's lack of experience, while Republicans denounced Clinton's indiscretions. With Florida's electoral votes still undecided on election night, it remained unclear who had won. The results revealed that Bush had won Florida by such a close margin that the state's constitution mandated a recount. A month-long series of legal battles led to the highly controversial 5–4 Supreme Court decision Bush v. Gore, which ended the recount.

As the result, Bush won 271 electoral votes, one vote more than the 270-to-win majority, despite Gore receiving 543,895 more votes (a margin of 0.52% of all votes cast). Arkansas, Arizona, Florida, Kentucky, Louisiana, Missouri, Nevada, New Hampshire, Ohio, Tennessee, and West Virginia were among the 11 states that Bush turned from Democratic to Republican.