Opinion by Thomas Balcerski

(CNN) -- With the 2020 presidential election less than a week away, the prospect once more looms of a challenger unseating an entrenched incumbent president. If Democratic candidate Joe Biden were to win when the results are finalized, he would make Republican President Donald Trump just the 11th incumbent in American history to try, but fail, to secure reelection.

In the last century, only three regularly elected incumbents -- Herbert Hoover, Jimmy Carter, and George H.W. Bush -- have lost their reelection bids. With incumbency so powerful a force, why did these three presidents fail?

Besides weathering touch economic times, each of these three failed incumbents demonstrated a fatal character flaw. Hoover followed a rigid way of thinking about the Great Depression afflicting the nation in the early 1930s; Carter exhibited a lethargic attitude about the economic malaise of the late 1970s; and Bush seemed out of touch with the problems facing the average American in the early 1990s.

Today's economic uncertainty is not a new feature of presidential elections. But when such crises occur during a sitting president's reelection campaign, voters have historically turned him out in favor of a challenger offering a new direction for the nation. In short, incumbents fail when they cannot convince the American people to stay the course.

Taken together, these embattled incumbents still provide a recipe for electoral disaster in American politics -- let's explore each in greater detail.

Herbert Hoover (1932)

Times were flush in America when the nation elected Hoover -- touted as the "Great Engineer" -- as president in 1928. Four years later, the country faced the worst economic crisis in its history, the Great Depression. The popular outcry against the president summoned new words into existence: "Hooverville" for a shantytown of the homeless and "Hoover Flags" for the turned out pockets of men waiting on bread lines.

But Hoover's own actions made matters far worse. To combat the depression, he promoted voluntarism with limited government intervention. Ignoring the problems facing Americans, the Republican Party platform that year merely called for a balanced budget and high protective tariffs.

Conflict on the streets of Washington also plagued the president. In July 1932, Hoover ordered the US Army, under the command of Gen. Douglas MacArthur, to clear out the "Bonus Army" encampment of World War I veterans. Then, as now, the optics were terrible.

Democratic challenger Franklin D. Roosevelt touted a "New Deal" for the American people. In response, Hoover defended his record across nine major addresses during the fall campaign. He rigidly insisted that his administration's response to the Great Depression had been sufficient. The issue before the people, Hoover declared, was "whether we shall go on in fidelity to American traditions or whether we shall turn to innovations, the spirit of which is disclosed to us by many sinister revelations and veiled promises."

An unprecedented 40 million Americans voted that November, yielding FDR an even larger popular victory than Hoover had won four years earlier. The Great Depression had done in the Great Engineer.

Jimmy Carter (1980)

Political life in America reached a new low in 1974 when President Richard Nixon resigned amid scandal. His successor, Gerald Ford, pardoned the ex-president, leaving him vulnerable to a Democratic challenger in 1976. Former Georgia Gov. Carter ran as an outsider and won a narrow victory.

By 1980, however, a global economic downturn had weakened the country. Oil shocks, rising inflation and industrial competition from abroad all took a toll. Abroad, the United States suffered a humiliating setback when Iranian militants took Americans hostage at the US embassy in Tehran.

Self-inflicted wounds also hurt the incumbent. In 1979, Carter described a "crisis in confidence" affecting the country. For its pessimistic tone, the address was dubbed the "malaise speech." To make matters worse, Carter asked for the resignation of his entire Cabinet, and five members acceded to the demand.

Republican challenger Ronald Reagan, by contrast, projected a sunny optimism, famously declaring recovery happens "when Jimmy Carter loses his" job. Carter fought back, warning of unregulated economic policies and cutbacks under a Reagan presidency, but it proved insufficient.

As the 1970s yielded to the 1980s, the nation chose a new direction, handing Reagan a resounding victory over the incumbent Carter. The peanut farmer from Plains could not convince the nation that he deserved another four years.

George H.W. Bush (1992)

The nation elected Bush with a wave of popular support in 1988. Like Hoover before him, Bush followed two terms of Republican control of the White House. But by 1992, a sharp recession had set in, leaving many Americans out of work and facing difficult times.

With the government facing revenue shortfalls, Bush went against his own campaign rhetoric -- his "read my lips" promise to not raise taxes -- and increased taxes in 1991. Although he led the nation through the first Gulf War in 1991, the president's approval rating continued to drop leading into the election year of 1992.

Political controversies also hurt. The nomination of Clarence Thomas to the Supreme Court, during which Anita Hill accused him of sexual harassment, rankled. When combined with domestic challenges, such as the Los Angeles riots in the spring of 1992, Bush was the definition of an embattled incumbent president.

Democratic challenger Bill Clinton proved popular, leading many to choose the younger candidate and informal motto: "It's the economy, stupid." Bush also likely lost votes to the third-party candidate Ross Perot. Although no candidate won a majority of the popular vote in November, Clinton secured enough electoral votes to become president.

Bush, the last former vice president to become president, was also the first sitting vice president to win election to the presidency since Martin Van Buren in 1836 (about which he enjoyed reminding reporters). Yet Bush could not win reelection in 1992 for similar reasons to his long-ago predecessor -- an economic downturn had soured the American people against him.

The 2020 election has the potential to be historic on a number of levels. No former vice president has ever unseated an incumbent president, as Biden threatens to do. If Trump loses in November, he will break the two-term presidential cycle in place since 1992, possibly setting the stage for a major realignment in American politics.

Will Biden suffer the same fate as his close friends John McCain, who ran and lost against then-President Barack Obama, and John Kerry, who ran and lost against then-President George W. Bush? Or will Trump be the next in a long line of embattled incumbents who fail to obtain a second term? The nation -- and the entire world -- eagerly awaits an answer.