(CNN) If the day ends in a "y" it's a good bet that Joe Biden has stumbled into yet another campaign trail gaffe.

The error-prone Democratic front-runner is now caught in a fresh self-inflicted storm over a poignant story he told about an Afghan war hero that seems a mishmash of three separate tales.

This after he assured a rapt crowd in New Hampshire last Friday about a story later fact-checked by The Washington Post: "This is the God's truth. My word as a Biden."

His string of recent faux pas is occurring in an utterly chaotic political environment because of President Donald Trump.

Biden's misspeaks, misrememberings and other gaffes are not the same as Trump's purposeful daily assaults on the truth.

But they are triggering a debate about the nature of truth in politics and about how voters should distinguish between Biden's slips and the President's arguably more serious habit of bending facts at a historic rate.

The cavalcade of lies uttered by the President has blown to smithereens the traditional metrics of assessing a candidate's fealty to the truth and the consequences of such malfeasance. Yet the exposure of the President's habitual lying has not disqualified him politically. To the contrary, he often prospers by creating his own reality into which loyalists can buy.

As a result of this new era of shredded fact, the 2020 campaign is unfolding at a historic inflection point.

Every word candidates utter is being parsed for falsehoods like never before by armies of media fact checkers conscripted to meet the challenges posed by Trump.

Yet it's also a moment when truth in politics appears more devalued than ever, since the President stands as an example that lying need not be fatal to a political career.

In a surreal moment on CNN's "Cuomo Prime Time" on Wednesday night, Trump's reelection campaign spokeswoman Kayleigh McEnany insisted Trump had never lied to the American people.

The President's behavior has led many media commentators to argue that politics has entered a post-truth era -- where there is no real penalty for lying.

It's hardly news that the former vice president is gaffe-prone: His blooper reel would probably stretch from his beloved Delaware to first-in-the-nation Iowa.

And many Democrats argue that fixating on Biden's verbal slips is a dereliction of duty by Beltway pundits when Trump seems to be tearing at the national fabric.

In fact, Biden made the case himself last December.

"I am a gaffe machine, but my God, what a wonderful thing compared to a guy who can't tell the truth," he said in Montana. "I'm ready to litigate all those things. The question is what kind of nation are we becoming? What are we going to do? Who are we?"

Former Democratic presidential candidate Howard Dean said Friday that Trump's serial untruths meant that lapses by other candidates were taken less seriously.

"Look, if the voters can forgive Donald Trump being corrupt and feathering his own nest with money, they can certainly forgive Joe Biden's few lapses in memory. I think Trump has lowered the bar so much ... I think the rules of the game have changed," Dean said on CNN's "New Day."

Is Trump unique, or is politics in a post-truth era?

One of the most important tests of the 2020 campaign will be whether Trump is unique and an outlier. Or has he pioneered a style of leadership that is not just unmoored from provable fact but can be emulated by other politicians and has lowered the bar on truth in public life?

Given these new dynamics, how then should Biden's scattered falsehoods, exaggerations and conflations be judged?

And should they undermine the central rationale of his campaign -- that he is best placed to beat Trump?

Biden is an especially interesting test case. As a Democratic rising star, the then-senator folded his bid for the 1988 presidential nomination over a plagiarism scandal.

He reluctantly quit after it emerged that he had lifted passages by former British Labour Party leader Neil Kinnock for a speech and was accused of other using other uncredited material.

"I am no less frustrated for the environment of presidential politics that makes it so difficult to let the American people measure the whole Joe Biden and not just misstatements I have made," he said at the time.

It's a measure of how the standards governing presidential politics have changed that Biden's offense may not have seemed so grave in the current era, nor the penalty so final.

It seems unlikely that a candidate seeking to oust the current President would have to pull out of the race for plagiarism, given that Trump is guilty of making more than 12,000 false statements in office, according to The Washington Post's count. CNN's Daniel Dale reported Wednesday that Trump had made 48 false claims in just the past six days.

Some Democrats have argued that Biden's gaffes are so quintessential that they are baked into his political image.

It's all part of the Irish blarney of a man whose heart always seems in the right place even if his foot is perpetually headed for his mouth. This is a guy, after all, who has mourned people who are still alive, told a man in a wheelchair to "Stand up, Chuck" and once called his old boss "Barack America."

Yet there's also a clear double standard.

Hillary Clinton was ridiculed by the Obama campaign in the 2008 Democratic race over her exaggerated claims of landing under sniper fire during the Bosnian war.

In Clinton's case, the falsehood reinforced existing claims that she had a habitual problem with the truth.

The Post reported that Biden got "the time period, the location, the heroic act, the type of medal, the military branch and the rank of the recipient wrong, as well as his own role in the ceremony" in the story about the Afghan veteran.

If Biden's story is not treated the same way, there will be more than a whiff of sexism.

Biden's tale also recalled an endearing yarn told by ex-President Ronald Reagan about a World War II aviator who stayed with a comrade who was too wounded to bail out of the crashing plane that took them to their deaths. Like Biden, Reagan was lauding the heroism of others. Still, it later emerged that he'd lifted the story from a movie, not a real life.

Biden insisted on Thursday that there was no reason for the fuss.

"I was making the point how courageous these people are, how incredible they are, this generation of warriors, these fallen angels we've lost," he told the Post in an interview.

"I don't know what the problem is. What is it that I said wrong?"

A distraction for Biden

Any day, however, that the story of the Biden campaign concerns gaffes is a bad day for his candidacy.

The vice president is presenting himself as the most experienced and street-smart Democrat who can best be trusted to handle the negative barrage that Trump is waiting to unleash.

But self-imposed controversies undermine that argument and offer an opening to question Biden's attitude toward the truth -- which Trump is sure to take with a outpouring of chutzpah.

The President has already raised questions about the 76-year-old Biden's age, calling him "sleepy" and speculating about his mental state -- despite the fact that Trump is also in his 70s.

Democrats are sure to accuse the media covering Biden's gaffes of false equivalency, much as they claimed that the focus in 2016 on Clinton's emails ignored much worse behavior by Trump.

There is also an undeniable question of degree. Is a messed-up Biden war story really in the same league as Trump's false claim that he won the popular vote in the 2016 election?

The latest Biden flap also unfolded after CNN, citing top Trump aides, reported that the President lied about getting phone calls from China about the trade war at the G7 summit.

Not telling the truth about a critical affair of state that affects the world economy surely outweighs the clumsy conflation in a campaign trail story.

Nuance and proportion, however, are always swamped in the heat of a presidential election campaign.