Twenty-second Amendment to the United States Constitution
The amendment prohibits any individual who has been elected president twice from being elected again. Under the amendment, an individual who fills an unexpired presidential term lasting greater than two years is also prohibited from winning election as president more than once. Scholars debate whether the amendment prohibits affected individuals from succeeding to the presidency under any circumstances or whether it only applies to presidential elections.
Marco Rubio
Rubio successfully ran for the United States Senate in 2010. In April 2015, Rubio announced that he would forego seeking re-election to the Senate to run for president. He suspended his campaign for president on March 15, 2016, after losing the Florida Republican primary to the eventual winner of the presidential election, Donald Trump. On June 22, 2016, Rubio reversed his decision not to seek re-election to the Senate; he went on to win a second term later that year.