Twenty-second Amendment to the United States Constitution
Since coming into force in 1951, the amendment has applied to six presidents who have been elected twice: Dwight D. Eisenhower, Richard Nixon, Ronald Reagan, Bill Clinton, George W. Bush, and Barack Obama. It has also applied to two who entered office intra-term due to their predecessor's death or resignation: Lyndon B. Johnson and Gerald Ford. Johnson became president in November 1963, following the assassination of John F. Kennedy, served out the final of Kennedy's term, and was elected to a full four-year term in 1964. Four years later, he briefly ran for a second full term, but withdrew from the race during the party primaries. Had Johnson served a second full term – through January 20, 1973 – the total length of his presidency would have been ; as it happened, Johnson died two days after this date. Gerald Ford, who became president in August 1974 following the resignation of Richard Nixon, served the final of Nixon's term, and attempted to win a full four-year term in 1976, but was defeated by Jimmy Carter. Johnson was eligible to be elected to two full terms in his own right, as he had served less than two years of Kennedy's unexpired term, whereas Ford was eligible to be elected to only one full term, as he had served more than two years of Nixon's unexpired term.
2020 United States presidential election
Beginning in August 2017, reports arose that members of the Republican Party were preparing a "shadow campaign" against Trump, particularly from the moderate or establishment wings of the party. Now late Arizona Senator John McCain said that "[Republicans] see weakness in this president." Maine Senator Susan Collins, Kentucky Senator Rand Paul, and former New Jersey Governor Chris Christie all expressed doubts in 2017 that Trump will be the 2020 nominee, with Collins stating "it's too difficult to say." Senator Jeff Flake claimed in 2017 that Trump is "inviting" a primary challenger by the way he is governing. Longtime political strategist Roger Stone, however, predicted in May 2018 that Trump may not seek a second term if he succeeds in keeping all of his campaign promises and "makes America great again".