Third-party candidates have long shaped U.S. presidential elections, often influencing the outcome and highlighting issues overlooked by the major parties. While they rarely win, their presence can significantly affect the political landscape.

One of the most notable early examples is Theodore Roosevelt's 1912 run as a Progressive Party candidate. After losing the Republican nomination to incumbent President William Howard Taft, Roosevelt's candidacy split the Republican vote, enabling Democrat Woodrow Wilson to win the presidency. Roosevelt's campaign garnered 27% of the popular vote, among the highest percentages ever for a third-party candidate.

In 1968, George Wallace of the American Independent Party won 13.5% of the popular vote and five Southern states' electoral votes. Wallace's pro-segregation platform attracted voters disenchanted with the civil rights policies of both major parties, showcasing the influence a third-party candidate can wield on regional and national politics.

In recent times, Ross Perot's independent candidacy in 1992 and subsequent Reform Party run in 1996 had significant impacts. Perot focused on the Federal deficit and economic issues, attracting voters from both major parties. In 1992, he received 19% of the popular vote, which many analysts believe siphoned votes away from incumbent President George H.W. Bush, aiding Bill Clinton's victory.

Ralph Nader's Green Party candidacy in 2000 is another example. Nader's campaign, emphasizing environmental issues and corporate reform, drew critical votes away from Democrat Al Gore in crucial states like Florida. Gore's narrow loss to George W. Bush in Florida, and thus the presidency, is often attributed to Nader's presence in the race.

Despite the significant structural challenges they face in the U.S. political system, third-party candidates continue to make their mark. The Electoral College and 'winner-takes-all' voting system in most states, along with ballot access laws, debate inclusion criteria, and campaign financing regulations, all pose hurdles. Yet, these candidates persist, undeterred by the odds stacked against them.

In the 2024 presidential election, candidates like Robert F. Kennedy Jr. and others have continued this tradition, bringing attention to issues such as public health, environmental policies, and corporate influence, which are often underrepresented in mainstream political discourse, yet unable to qualify to participate in debates or be listed on many state ballots.

While they may not often win, third-party candidates have the potential to significantly shape policy. Their campaigns can force major parties to address issues they might otherwise ignore, bringing attention to critical topics and influencing the platforms of the Democratic and Republican parties. For instance, Perot's focus on the deficit influenced both significant parties' economic policies in the 1990s. Nader's emphasis on environmental issues helped push the Democrats to adopt more robust ecological policies.

Third-party candidates have a nuanced but significant impact on U.S. presidential elections. Though they have yet to win a Presidential election, their campaigns can alter election outcomes, bring attention to specific issues, and influence major parties' policies. Understanding their role provides a deeper insight into the complexities of American electoral politics.