In fewer than 100 days, Jimmy Carter will turn 100, making him the first former president to become a centenarian.

When his office announced more than 16 months ago that Carter had entered hospice care at his home in Plains, Ga., it was widely assumed that the 39th president had only days or weeks to live. In the United States, 25 percent of patients die within five days of enrolling in hospice; half pass away within 17 days.

But Carter is a tough survivor. At age 90, he was diagnosed with cancer of the liver and the brain, but he went on to beat them both. He broke his hip and pelvis in falls five years ago but successfully recovered. Carter’s longevity and physical resilience are just two of the factors that make his extended post-presidency — he left the White House after one term more than 43 years ago — so remarkable.

Over the years I have written a number of times to praise choices Carter has made since he was defeated for reelection in 1980. I admire his devotion to Habitat for Humanity and the hundreds of hours he and his late wife, Rosalynn, spent helping to construct homes for people in need. I applaud his efforts, through the Carter Center he established in 1982, to eradicate a devastating disease called Guinea worm. Above all I have applauded his refusal to spend his post-White House years — unlike every other president in the modern era — lining his pockets with millions of dollars accumulated through speaking fees.

Unfortunately, not everything about Carter’s long tenure as a former president has been so commendable. Especially unpleasant and damaging was the frequency with which he derided his successors and their policies.

Virtually from the moment Joe Biden became president, he has been attacked, critiqued, and mocked by his predecessor, Donald Trump. Such behavior is typical of Trump. But for most of the modern era it has been decidedly atypical of ex-presidents. After leaving the White House, Lyndon Johnson didn’t trash Richard Nixon; Gerald Ford didn’t publicly undercut Carter; and George W. Bush was scrupulous about not criticizing Barack Obama.

The one exception to the rule was Carter, who lashed out repeatedly at the men who succeeded him in the nation’s highest office.

Jared Cohen devotes a chapter to Carter in Life After Power, a fascinating new history of seven former presidents and what they did with their lives after their White House tenures came to an end. A key theme of Carter’s post-presidency was the resentment he felt over losing his bid for a second term. His greatest failing in office, he said in an interview, was “allowing Ronald Reagan to become president.”

Carter made no attempt to disguise those feelings.

When the Egyptian leader Anwar Sadat was assassinated in 1981, Reagan asked Carter to represent the United States at the funeral in Cairo and afterward invited Carter to a private meeting at the White House. But on his way to the Oval Office, the former president excoriated his successor, calling him “an aberration on the political scene” and deriding his “false and erroneous promises.”

Carter “seldom passed up an opportunity to lambaste Ronald Reagan,” Cohen writes. But the lambasting didn’t end when Reagan’s presidency ended. Carter openly undermined the elder Bush’s efforts to liberate Kuwait from Iraqi dictator Saddam Hussein during the Gulf War, going so far as to lobby the UN Security Council to oppose military intervention. When Bill Clinton sought to pressure North Korea to end its illegal nuclear weapons program, Carter went on CNN to undercut the White House position. After 9/11, Carter went out of his way to rebuke the second President Bush, calling his foreign policy “the worst in history.” He later said his harsh words had been “careless” — but he also wrote a column in The New York Times taking pride in what he called his “pariah diplomacy” to resist the administration’s efforts abroad.

Later still came an attack on the Obama administration’s “cruel and unusual” use of drones to target terrorists abroad. “The United States,” Carter declared in 2012, “is abandoning its role as the global champion of human rights.” The following year, angry over revelations of Obama’s domestic surveillance program, Carter told an interviewer that “America has no functioning democracy at this moment.” As for Trump, Carter told a TV audience that he was “an illegitimate president” who really lost the [2016] election but “was put into office because the Russians interfered on his behalf.”

The most shining achievements of Carter’s post-White House career have been those that steered clear of partisan politics — his efforts to end sickness, house the poor, and monitor foreign elections. His inability to restrain the urge to berate his successors was far less admirable. The 39th president’s virtues were considerable. Alas, so were his flaws.