So here now is a list of 10 people who could have become President of the United States:
10. Robert F. Kennedy
Senator of New York, US Attorney General, and brother of President John F. Kennedy, Robert F. Kennedy announced on March 16, 1968 that he was running for President the United States. Unfortunately, on June 5, 1968, he was assassinated. Many people to this day speculate about whether or not he would have been elected president if he had not been assassinated.
9. John McCain
Senator John McCain of Arizona has run for president twice. In 2008 he was defeated soundly Barack Obama, and back when he ran in 2000, he didn't even receive the Republican nomination, but many people have speculated that if he had won the Republican nomination in 2000, he would have defeated Al Gore, and by a much wider margin then what George W. Bush did.
8. Thomas E. Dewey
While it's true that New York Governor Thomas E. Dewey didn't actually come close to becoming president, many in the media at the time had speculated during the voting returns that he was going to defeat President Truman. One newspaper, the Chicago Daily Tribune, was so convinced that Governor Dewey was going to win, that they published in their headlines that Dewey had defeated Truman, which lead to this iconic photo:
7. Hillary Clinton
In 2008 the former first lady and New York senator ran for the Democratic nomination for President of the United States. She barely lost the nomination to Barack Obama, and due to the fact that the Republicans were so unpopular at the time, if she had won the nomination, she could very well have become the first female President of the United States.
6. Henry A. Wallace
Basically this is a matter of fate. If Franklin D. Roosevelt had chosen to keep his Vice President of his third term, Henry Wallace, and had not chosen Harry Truman to be his Vice President, Henry Wallace would have become the 33rd President of the United States after President Roosevelt died.
5. Hannibal Hamlin
Once again, this is a matter of fate. Hannibal Hamlin was Abraham Lincoln's first Vice President, and if President Lincoln had decided to run with Hamlin again instead of Andrew Johnson, he would have become the 17th President of the United States after President Lincoln had been assassinated.
4. Winfield Scott Hancock
While General Winfield Scott Hancock may have been solidly defeated by James A. Garfield in the 1880 presidential election, in terms of electoral votes, he only lost the popular vote by less than 2,000 votes. It is entirely plausible that if General Hancock had received a few more thousand votes, he might have become the 20th president of the United States.
3. Al Gore
Vice President Al Gore barely lost to George W. Bush in the 2000 presidential election. In fact he had only lost by five electoral votes, and had actually won the popular vote. He had also only lost the state of Florida, the state that ultimately resulted in him losing the election, by 537 votes. Even to this day some people still won't acknowledge George W. Bush's victory in that election, and continue to blame the Supreme Court and Ralph Nader (who many consider to be a spoiler in that election) for Al Gore's lose.
2. Samuel J. Tilden
New York Governor Samuel Tilden almost defeated Rutherford B. Hayes in the 1876 presidential election. He actually did win the popular vote, but lost the electoral vote by one vote. In fact, 20 of the electoral votes in three states were disputed, but were eventually awarded to Rutherford B. Hayes. This is perhaps the closest that any one has come to being elected president, and still never becoming President of the United States.
1. Benjamin Wade
Senator Benjamin Wade was President Pro Tempore of the US Senate at the time of President Andrew Johnson's impeachment trial, and at that time in our country, our laws stated that the President Pro Tempore of the US Senate was second in line of presidential succession. If only one vote had gone against President Johnson, then Benjamin Wade would have become the 18th President of the United States.