ATLANTA (AP) — There’s plenty of worry among Democrats about whether 81-year-old President Joe Biden is up to the job itself or the task of defeating Donald Trump.

Previous presidential campaigns offer lessons. None convey reasons for optimism.

Going back to Lyndon B. Johnson in 1968, several presidents eligible for reelection faced significant primary challenges or questions about whether they should run again. George H.W. Bush, Jimmy Carter and Gerald Ford pushed forward and won their nominations, only to be defeated in November. Johnson opted to withdraw — and Democrats lost anyway.

Biden had no real primary fight. But his allies now acknowledge how poorly the president performed in his debate against Trump. They’ve fretted privately about Biden’s ability to serve until he is 86, and, more immediately, whether he can keep the job by defeating the Republican former president — himself a 78-year-old saddled with a felony conviction, other indictments and voter concerns over his values and temperament.

The warning from history is ominous: Incumbent presidents still working to consolidate and reassure their own party this late in a first term typically do not get a second.

An Ivy League-educated Episcopalian, Bush was a moderate Republican and never a favorite of the Christian right or anti-tax, small-government activists.

Bush appealed to the right flank ahead of his victory in 1988, saying, “Read my lips: no new taxes.” He was riding high in 1990 after a quick U.S. military victory drove Iraq and Saddam Hussein from oil-rich Kuwait. Within months, though, Bush broke his tax pledge, the U.S. economy began to falter (albeit mildly in retrospect), and the president grew vulnerable.

Primary challengers emerged, notably Steve Forbes, an anti-tax crusader, and commentator Pat Buchanan, a Christian conservative. Bush won every primary but many by unimpressive margins. Buchanan, rather than endorsing Bush enthusiastically, used his GOP convention speech to enlist religious conservatives in a “culture war” against Clinton, liberals and secularism — standard Republican rhetoric today but a more divisive tone alongside Bush’s talk of a “kinder, gentler” nation.

Democratic challenger and Arkansas Gov. Bill Clinton hammered Bush as out of touch with middle-class Americans. And billionaire Ross Perot entered the contest as an independent.

On Election Day, 62.6% of voters opted against Bush. Clinton won 370 electoral votes, the second-highest total for any Democrat since 1964.

A former Georgia governor, Carter was a moderate Southerner from outside the liberal Democratic power structure. His 1976 nomination and eventual victory over the Republican incumbent Ford was less about ideology, though, and more about Carter’s promise never to lie to Americans disillusioned after Vietnam and the Watergate scandal.

Legislative successes followed, but Carter rankled Washington Democrats. Global inflation, U.S. unemployment and interest rates climbed, and Carter’s popularity fell.

“Carter was never expected and accepted by the establishment,” said Joe Trippi, a 1980 Kennedy campaign staffer.

Sen. Ted Kennedy mounted a primary challenge in 1980, inspiring young progressives like those who had once adored his slain older brothers. Carter famously said of Kennedy, “I’ll kick his ass.” The president won enough delegates for the nomination, even as the Iran hostage crisis compounded his problems.

Yet in defeat, Kennedy used his convention speech more to rouse his own supporters rather than reconcile with the incumbent. “The work goes on, the cause endures … and the dream shall never die,” Kennedy declared, exposing Carter’s weaknesses.

Against Republican Ronald Reagan, Carter carried just six states and Washington, D.C.

Reagan won two general election landslides, but the foundation was his 1976 primary challenge against Ford.

A mild-mannered Michigander, Ford had a unique path to the White House. President Richard Nixon elevated him from House leadership to the vice presidency in 1973 after corruption forced Spiro Agnew’s resignation. Ford ascended to the presidency a year later when Nixon resigned because of Watergate.

Controversially, Ford pardoned Nixon. He faced inflation, high unemployment and roiled energy markets. And he had to prepare quickly to seek his own election, never having been part of a national campaign.

Ford hailed from Capitol Hill’s center-right, a Republican cohort that mostly accepted the federal government’s expanded scope since Franklin Delano Roosevelt’s New Deal. Reagan, meanwhile, was corralling conservatives who never embraced FDR’s America and blanched at the Civil Rights Movement and social revolutions of the 1960s and 1970s.

In the ’76 primaries, Ford won 27 contests to Reagan’s 24. That gave the incumbent 1,121 delegates, just 43 more than the insurgent challenger. Reagan had dominated most primaries in the South, the most conservative region of the country.

In the fall campaign, a wounded Ford made a late comeback against Carter but fell short. Carter carried the South. And Reagan was positioned to take the Republican mantle four years later.

Ford, Carter and Bush are not perfect parallels for 2024: Biden did not draw a credible primary challenge and, even with the debate fallout, he has a well of personal goodwill across his party. Perhaps the best comparison, then, is Johnson.

The assassination of John F. Kennedy thrust Johnson into the Oval Office in November 1963. Known as LBJ, the colorful Texan trounced Republican Barry Goldwater in 1964. Johnson amassed the most sweeping legislative record since FDR: the Civil Rights Act of 1964, Voting Rights Act of 1965, Medicare and Medicaid. But Johnson vastly expanded U.S. involvement in Vietnam — and lied to the country in the process. He also found himself unable to shepherd Americans through social changes of the era.

Presidential campaigns were shorter then, so it was not until March 31, 1968, that Johnson mulled his sagging standing and announced his intentions. After weak showings in early primaries, which were not then binding affairs, Johnson said in an Oval Office address, “I shall not seek, and I will not accept, the nomination of my party for another term as your president.”

What followed, though, is not necessarily encouraging for Democrats hoping to hear the same from Biden.

New York Sen. Robert F. Kennedy — whose son, Robert F. Kennedy Jr., is mounting an independent presidential bid this year — joined a spirited Democratic nominating fight and secured momentum by winning the California primary in June. But he was assassinated in Los Angeles minutes after his victory speech.

Democrats were left with a raucous convention in Chicago — also the site of the 2024 convention. They chose Vice President Hubert Humphrey to take on Nixon, the Republican former vice president who had lost to John F. Kennedy in 1960 and then dropped the 1962 California governor’s race.

Neither Nixon nor Humphrey were broadly popular, and the resulting general election was close, with independent George Wallace a key factor. Nixon outpaced Humphrey by about 500,000 votes out of 73 million cast, and he secured 301 electoral votes.

Seven months after a beleaguered Democratic president stood down, his party met defeat. Republicans, with a president-elect who would one day resign in disgrace, had their comeback story.

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