Rambling Joe' Biden was forgiven his gaffes - no longer

President Joe Biden has for years been called the rambling uncle of US politics, prone to verbal slips and meandering sentences, but now the whole world is watching.

Everything changed at his disastrous debate last month with Donald Trump, when more than 50 million viewers were confronted by a president who went on tangents, failed to finish phrases and looked altogether lost.

But Biden's struggles with communication are hardly new.

He overcame a childhood stutter that can resurface, and he went on to earn a reputation for both blunders and verbosity in a half-century career as a senator and vice president to Barack Obama.

Biden, now 81, was for decades a leading figure of the Senate where lawmakers can speak at length to an often half-empty chamber, with little to stop them.

And he became one of its most notable practitioners. "I want to note that for maybe the first time in history, Biden is 40 seconds under his time," a committee chairman said in 2006 after a brief 30-minute Biden monologue. Too much talking cost him in his failed 1998 presidential campaign where he became known for going on about hobby horse subjects like train travel or his childhood in Scranton, Pennsylvania - subjects he still loves today.

His second candidacy for president in 2008 also went nowhere, earning him a "Ramblin' Joe Biden" ribbing from comedian Robin Williams.

"Joe is like your uncle who is on a new drug and doesn't have the dosage right," Williams joked 15 years ago.

When Biden became vice president in 2009, it was widely reported that Obama aides would mock Biden's lack of rhetorical style and precision.

"I don’t remember exactly what Joe was referring to - not surprisingly," Obama quipped in his first press conference as president.

But after eight years as vice president, and after the four tumultuous years of Donald Trump in the White House, Biden’s verbal shortcomings came to be seen as a familiar and generally innocuous facet of US politics.

"Rambling, stumbling, bumbling - that's something we've had in a lot of political figures, including beloved political figures - and Joe Biden was one of those,” said pop culture and media professor Robert Thompson of Syracuse University.

"But there has been a marked difference between what we saw, in a ruthless, unforgiving way, in the debate" and Biden’s usual foibles, he told AFP.

In the debate, Biden was not only meandering and vague, but also out of breath as he mumbled phrases and looked on aimlessly, mouth agape.

Since that night, Thompson said, viewers have been hanging on Biden’s every appearance, ready for the next howler or non sequitur.

Political reporters in Washington are doubly vigilant, given criticism that they failed to adequately report on the effects of ageing on the president before the debate.

"It is simply astounding for the entire country, including its most seasoned reporters, to be as shocked as everyone was by the ugly and painful reality of Biden’s debate performance,” wrote Jill Abramson, former executive editor of the New York Times, on the Semafor website.

now has a high bar to pass at every public event, and that new reality was clear on Thursday when he gave a press conference after a NATO summit in Washington.

It became must-see-TV, and his usual selection of slip-ups went viral on social media as supposed proof that he was not fit for office.

Errors like an unfortunate mention of his "Vice President Trump" may have been forgotten with a few eye-rolls years ago, but not now.

"Donald Trump is using that to mock your age and your memory," a reporter shouted to him just moments after the fumble.

"How do you combat that criticism?"