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.
2020 United States Senate elections
One-term incumbent Democrat Cory Booker was re-elected in 2014; Booker first took office after winning a 2013 special election. Booker, who is running for President in 2020, could run for both President and re-election to the Senate as New Jersey election laws allow candidates to simultaneously run for two offices. Should Booker choose to forgo a Senate run in 2020, though, potential Democratic nominees include incumbent governor Phil Murphy and incumbent Congressmen Donald Norcross and Josh Gottheimer.