On Oct. 16, 11 months after defeating her, President Trump tweeted another of his regular insults about his 2016 opponent, Democrat Hillary Clinton. Sandwiched between boasts about his presumed role in the stock market’s rise and his rally in South Carolina, Trump wrote: “I was recently asked if Crooked Hillary Clinton is going to run in 2020? My answer was, ‘I hope so!’”

Putting aside the reckless braggadocio — and blatant sexism — inherent in such a statement, the entire scenario seemed absurd. Most pundits (and most of the American public) discount the idea of Clinton running in 2020, doubtful she could win the Democratic nomination, let alone the election, after her stunning loss to Trump. Clinton herself has stated that her political career is over, that she is more interested in speaking out against Trump as a private citizen.

Nevertheless, Trump should be careful what he wishes for. Clinton might not be a potential candidate now, but the political winds can change quickly. Recent American history is rife with presidential contenders who lost the primary or general election and then went on to become a candidate in subsequent elections. Dissatisfied with the politics of the day, lured by name recognition and preexisting loyalties, the public gave each of these candidates multiple chances at the presidency and handed several the keys to the White House.

Add to that Trump’s abysmally low approval ratings and inability to deliver on signature campaign promises (building a border wall, ending NAFTA and repealing the Affordable Care Act, to name a few), and Clinton could once more emerge as a serious challenger.

Political comebacks — even seemingly impossible ones — are actually regular occurrences in modern American politics. Richard Nixon remains the most (in)famous example. Nixon narrowly lost to John F. Kennedy in the 1960 election — only about 110,000 votes nationwide separated them — then ran for governor of California in 1962, only to lose that election. Nixon told the press after his defeat in 1962 that he was done with politics. “You don’t have Nixon to kick around anymore,” he proclaimed.

But when Lyndon Johnson trounced conservative Republican Barry Goldwater in 1964 (LBJ won all but six states), Nixon recast himself as the person best able to unite the factions within the GOP. Nixon’s chances were bolstered by a widespread opposition to the Vietnam War that fueled voters’ desire for a change in the White House. Nixon also courted Southern whites — who traditionally voted Democrat — dismayed over civil rights legislation and urban riots in the 1960s. Nixon ran for president again in 1968, capturing the Republican nomination and then the presidency.

Ronald Reagan shifted the Republican Party back to the right in 1980, but it wasn’t his first bid for the presidency. Reagan vied with Nixon in 1968 during the presidential primaries and at the Republican convention, and then challenged Gerald Ford in 1976 for the Republican nomination, where Reagan won enough key states, including Texas and California, to ensure a contested Republican convention that summer. Ford won the nomination at the convention, but after he lost to Jimmy Carter, Reagan became the favorite among Republicans in 1980. Reagan might have lost in 1980, too, had it not been for “stagflation” and the fall of detente between the United States and Soviet Union. High unemployment, inflation rates and oil prices in the late 1970s convinced many Americans that Reagan was right: Government, or at least President Carter, was the problem.

The Democrats have also had their own share of political rebirths since the 1950s, although their experiences may serve more as a caution to Clinton than an inspiration. Adlai Stevenson was nominated for president twice, and almost a third time. His first chance for the presidency came in 1952 where he lost to Dwight Eisenhower — badly. Stevenson won only 89 electoral votes. His humiliating defeat did not deter Democrats from nominating him again in 1956, but the Korean War was over, the economy was booming and Republicans claimed responsibility for both. The result was Stevenson achieving an even more abysmal showing than he had in 1952 — winning only 73 electoral votes.

After his second loss to Eisenhower, Stevenson (like Clinton) announced publicly he would not run in 1960. His decision did not stop his closest supporters, including Eleanor Roosevelt, from creating a “Draft Stevenson” movement at the 1960 Democratic convention. Many Democrats still believed Stevenson was the sole progressive who appealed to both the left and right wings of the party — to the radicals on workers’ rights and civil rights, as well as to southern Democrats. Stevenson changed his mind, but it was too late. John Kennedy was already the clear favorite among Democratic delegates.

Another Democratic candidate in 1960, Minnesota Sen. Hubert Humphrey, was considered by members of his party to be “too liberal” for the presidency. Humphrey lost to the more moderate Kennedy in the 1960 primary, where he was outmatched by Kennedy’s money and political swagger. However, by 1968, now-Vice President Humphrey was the nominee.

Humphrey lost in 1968 for the same reason Nixon won: Vietnam. Voters viewed Humphrey as a patsy of Johnson and the war he (and Democrats) made. Humphrey went from the leading liberal to the liberals’ worst problem in eight short years. Humphrey ran again in 1972, but the 1968 election (and the chaos at the Democratic convention in Chicago that year) cast a pall over his liberal legacy, and the more left-wing George McGovern received the nomination

These are just a few examples from postwar American history. If Americans, including Trump, looked back further, they would find William Jennings Bryan, who was nominated three times for the Democratic ticket (1896, 1900 and 1908), or Democrat Al Smith, who lost the nomination in 1924 but won it in 1928 — and overcame white nationalist, anti-Catholic sentiments in the process. Not to mention Republican Theodore Roosevelt, who ran on the Progressive Party ticket in 1912 after leaving politics in 1909.

Clinton could easily be counted among this distinguished group (in fact, she already is, having lost the Democratic nomination in 2008). Clinton still retains significant support within her party, and Democrats currently have no clear front-runner to replace her. Clinton and her husband, former president Bill Clinton, have numerous financial backers willing to support her campaign, and the former nominee has a vibrant, large, motivated base of supporters angry at Trump, Russian interference in the election and former FBI director James B. Comey — in their minds, the collective robbers of Clinton’s presidency. Moreover, as Trump hates to be reminded, Clinton won the popular vote.

While Trump welcomes a Clinton challenge in 2020, he may find himself regretting it if voters come to believe they made a mistake and look to Clinton to rectify the wrong. Like Nixon and Reagan, Clinton can win the presidency in 2020 thanks to a combination of demographic and electoral shifts among voters and uncertainty about their futures. If Trump pulls Americans into a new economic recession or an unpopular war or fails to follow through on his rhetoric (which looks likely), Hillary Clinton’s time out of office might prove temporary.

It would not be the first time in American history.