ALTOONA, IA - AUGUST 21:  Democratic presidential presidential candidate, former Vice President Joe Biden speaks at the Iowa Federation Labor Convention on August 21, 2019 in Altoona, Iowa. Candidates had 10 minutes each to address union members during the convention. The 2020 Democratic presidential Iowa caucuses will take place on Monday, February 3, 2020.(Photo by Joshua Lott/Getty Images)
Joshua Lott/Getty Images North America/Getty Images
ALTOONA, IA - AUGUST 21: Democratic presidential presidential candidate, former Vice President Joe Biden speaks at the Iowa Federation Labor Convention on August 21, 2019 in Altoona, Iowa. Candidates had 10 minutes each to address union members during the convention. The 2020 Democratic presidential Iowa caucuses will take place on Monday, February 3, 2020.(Photo by Joshua Lott/Getty Images)
Now playing
02:10
Biden tells emotional war story, but there's a big problem with it
Joe Manchin
CNN
Joe Manchin
Now playing
02:03
'I never thought in my life ...' Why Manchin won't walk away from bipartisanship
Gaetz speaks to members of the media outside the hearing Michael Cohen, former attorney and fixer for President Donald Trump, testifies at before the House Committee on Oversight and Reform at Rayburn House Office Building February 27, 2019 on Capitol Hill in Washington, DC. Last year Cohen was sentenced to three years in prison and ordered to pay a $50,000 fine for tax evasion, making false statements to a financial institution, unlawful excessive campaign contributions and lying to Congress as part of special counsel Robert Mueller's investigation into Russian meddling in the 2016 presidential elections.
Alex Wong/Getty Images
Gaetz speaks to members of the media outside the hearing Michael Cohen, former attorney and fixer for President Donald Trump, testifies at before the House Committee on Oversight and Reform at Rayburn House Office Building February 27, 2019 on Capitol Hill in Washington, DC. Last year Cohen was sentenced to three years in prison and ordered to pay a $50,000 fine for tax evasion, making false statements to a financial institution, unlawful excessive campaign contributions and lying to Congress as part of special counsel Robert Mueller's investigation into Russian meddling in the 2016 presidential elections.
Now playing
06:11
'Bombastic, antagonistic, unapologetic': A look at Gaetz's political career
Former House Speaker John Boehner attends a ceremony to unveil a portrait of himself on Capitol Hill, Tuesday, Nov. 19, 2019 in Washington.
Michael A. McCoy/AP
Former House Speaker John Boehner attends a ceremony to unveil a portrait of himself on Capitol Hill, Tuesday, Nov. 19, 2019 in Washington.
Now playing
02:42
Boehner says Republican colleague held 10-inch knife to his throat outside House floor
President Joe Biden, accompanied by Vice President Kamala Harris, and Attorney General Merrick Garland, speaks about gun violence prevention in the Rose Garden at the White House, Thursday, April 8, 2021, in Washington.
Andrew Harnik/AP
President Joe Biden, accompanied by Vice President Kamala Harris, and Attorney General Merrick Garland, speaks about gun violence prevention in the Rose Garden at the White House, Thursday, April 8, 2021, in Washington.
Now playing
02:05
Biden calls for ban on assault weapons
CNN
Now playing
02:22
Biden: High-speed internet is infrastructure
AFP/Getty Images
Now playing
03:24
Donald Trump breaks his silence on Matt Gaetz
CNN/WLOX
Now playing
01:43
'He says the quiet part out loud': Borger reacts to GOP election official's remark
AFP/Getty Images
Now playing
02:30
Haberman: Trump had to be talked out of defending Matt Gaetz
CNN
Now playing
03:26
Georgia's Lt. governor says elections law was a result of Trump's misinformation
Now playing
02:38
GOP lawmakers can't give examples of why states need anti-transgender sports bills
CNN
Now playing
03:04
Avlon reacts to McConnell's advice to corporations
WASHINGTON, DC - APRIL 06:  U.S. President Joe Biden delivers remarks on the state of vaccinations in the U.S. in the State Dining Room of the White House April 6, 2021 in Washington, DC. President Biden announced that states should make all adults eligible for COVID-19 vaccine by April 19.  (Photo by Alex Wong/Getty Images)
Alex Wong/Getty Images North America/Getty Images
WASHINGTON, DC - APRIL 06: U.S. President Joe Biden delivers remarks on the state of vaccinations in the U.S. in the State Dining Room of the White House April 6, 2021 in Washington, DC. President Biden announced that states should make all adults eligible for COVID-19 vaccine by April 19. (Photo by Alex Wong/Getty Images)
Now playing
01:12
'Smarten up': Biden admonishes states' restrictive voting laws
WAVE
Now playing
01:27
'It's stupid': McConnell's warning for corporate America
reality check thumb
reality check thumb
Now playing
02:48
John Avlon breaks down fraud claims among Trump donors
Now playing
06:22
Key figure in Gaetz extortion claims responds

Editor’s Note: Julian Zelizer is a professor of history and public affairs at Princeton University, and author of the forthcoming book, “Burning Down the House: Newt Gingrich, the Fall of a Speaker, and the Rise of the New Republican Party.”
Follow him on Twitter at @julianzelizer. The opinions expressed in this commentary are his own. View more opinion at CNN.

(CNN) —  

With a story he likes to tell on the campaign trail, former Vice President Joe Biden has once again triggered anxiety about his campaign.

Biden loves to share a memory about traveling to Afghanistan as vice president to mark the heroic actions of a Navy captain who didn’t want the honor. The problem, according to The Washington Post, is that “almost every detail in the story appears to be incorrect. … It appears as though the former vice president has jumbled elements of at least three actual events into one story of bravery, compassion and regret that never happened.”

The revelation has caused another stir. Critics pounced, warning that the misstatements point to Biden’s weakness as a candidate, which will come back to haunt Democrats in 2020. His willingness to play with the facts, the critics say, is the last thing that we need in the age of Trump.

In response, Biden rejects the criticism, insisting that the basic thrust of the story was true.

At some level, this is just one more campaign moment when a candidate makes a gaffe, the media pounces on it and an incident generates a 24-hour conversation before journalists move on.

But at another level, the revelation touches on some deeper questions about the Biden campaign. If “electability” is a candidate’s biggest calling card, debates about missteps are natural and inevitable.

Biden has a long history of making verbal statements that have become politically problematic, most famously with a plagiarism scandal that damaged his 1988 campaign. Democrats want to know how much of this they will be seeing in the fall of 2020 and how much fodder Biden will offer the Republican machine as they line up to decimate his character.

President Trump’s Twitter feed is already warmed up and ready to go. Given the stakes in the election, Democrats don’t want to take any big risks. The same sentiment that makes Biden the front-runner, the notion that he is best positioned to win, can also quickly turn into a liability with moments like these.

Playing fast and loose with the facts also relates to the problems that Biden’s Democratic rivals see in his long record in Washington. On a number of important issues, such as his opposition to school busing to promote integration in the 1970s or his controversial role in the Clarence Thomas hearings, many Democrats feel Biden has been on the wrong side of history. He went too far trying to placate the white male vote at the expense of African-Americans, women, Latinos and others who were becoming a bigger part of the Democratic party coalition.

The inaccuracy he exhibited with the Afghanistan story reflects, in their mind, the way he tries to cover up these elements of his own complex history. The same verbal exploits at work in this case are what he used to explain his alliance with segregationist Sen. James Eastland or his lukewarm response to allegations of sexual harassment against Thomas.

And then there is the issue few like to speak about: his age. At 76, Biden is not a young candidate. At several points in the race so far he has displayed signs that this can be a potential source of trouble. During the Democratic debates, Biden sometimes seemed to have difficulty, running out of steam in his response to Kamala Harris or flubbing the delivery of his campaign website.

Fears that he is not in the right shape for a rigorous campaign are never far from the surface. Even though his two biggest competitors, Sens. Bernie Sanders and Elizabeth Warren, are also older than 70, their energy and precision have pushed aside any similar concerns.

There are legitimate questions about whether Biden can withstand the brutal pace of a presidential campaign and, equally relevant, the presidency itself.

All of these fears come right to the surface with a story like this. In any other moment, these might be enough to quash a candidacy.

Yet Biden keeps moving forward and his polls remain solid. The reason is President Donald Trump. All of the ways in which Biden stumbles are nothing compared to what Americans see from the President, certainly in the eyes of most Democrats.

Get our free weekly newsletter

President Trump is the liar-in-chief. President Trump is the king of fogging the public record to hide key parts of his past. President Trump is the politician who is unstable, out of control and incapable of carrying out the responsibilities he holds.

With a president like this, at least thus far, many Democrats are willing to forgive Biden for flaws such as the Afghanistan story – and everything else – and they will still support his campaign. Even most of his progressive opponents would probably back him should the other candidates lose by the time of the convention.

Biden recognizes his problem but also puts it in context: “I am a gaffe machine,” he said last December, “but my God what a wonderful thing compared to a guy who can’t tell the truth.”

Yes, Trump is the juice that keeps the Biden campaign running strong. As long as the President keeps doing what he does, the serious concerns embedded in this smaller story about his time as vice president will keep fading into the background.