As Joe Biden leads the race heading into the next set of primary votes on Tuesday, he has unleashed a rarely used weapon in what has become a two-man battle for the Democratic presidential nomination: Brevity.

Mr Biden's event in St Louis, framed by the Gateway Arch, clocked in at about seven minutes on Saturday. A short time later, at a windswept event in Kansas City, people were streaming towards their cars after Mr Biden wrapped up in 12 minutes. His longest speech of the weekend, in the gym of Tougaloo College in Jackson, Mississippi, didn't quite make 15 minutes.

It is a seismic shift for Mr Biden who in five decades of political office and three White House runs has never had a reputation for breviloquence. It's a habit perhaps nurtured in the Senate, which prides itself on limitless debate and has a special term - filibuster - for talking endlessly.

In his shortened speeches, Mr Biden still touches on his platform points, takes subtle jabs at Bernie Sanders and makes more than a few passing references to former president Barack Obama - he just does it all much faster.

“Senator Sanders is a good guy,” Mr Biden said in Jackson, speaking from a teleprompter, as he did at all his campaign rallies this weekend. “He says we need a record turnout to beat Donald Trump. And he's absolutely right. And we're going to be the campaign to do it.” He added that “155,000 more votes were cast in the South Carolina primary than four years ago, and guess what? They voted for us.”

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Mostly gone are the not-so-brief diversions into Biden family lore, wonky dispositions on complex policy points and anecdotes about the history of the phrase “rule of thumb”. Combined, the Bidenisms have often put his campaign events dangerously close to exceeding the running time of a feature-length movie.

The less Mr Biden strays from his streamlined and teleprompted remarks, the less likely he is to make a gaffe that could ricochet around the Internet. Even with his shorter speeches, he's made an unforced error or two. In his Sunday remarks at New Hope Baptist Church which lasted 14 minutes, he derided Mississippi's former governor for not accepting Medicare-for-all - which happens to be Mr Sanders' chief policy proposal - instead of the Affordable Care Act.

Mr Biden's critics have seized on the length of his sometimes-meandering stump speeches and occasionally labyrinthine tangents as a sign that he lacks focus and sharpness. His supporters, though, see Mr Biden's willingness to talk for as long as people will listen as a strength, one that reflects his desire and ability to connect with voters.

When he was campaigning in New Hampshire before that state's primary on 11 February, Mr Biden occasionally took more time to answer a single question than the entire length of his seven-minute speech in St Louis.

At a town hall in Hudson, New Hampshire, a month ago, a woman told Mr Biden during the question-and-answer period that she had autism, asking what he would do to help her and others with disabilities.

What followed was a 10-minute response that touched on a range of subjects, from his son's military service in Kosovo to Medicare negotiations over prescription drug prices to an ailment called ankylosing spondylitis, a spinal disorder whose signature look Mr Biden briefly demonstrated for the audience.

“I had a son who, when he came home from Iraq - not Iraq, when he came from Kosovo,” Mr Biden said midway through the answer. “He was over there and he came home. It turns out he was exposed to significant bacteria. And it turns out he had a, he had a marker for ankylosing spondylitis. Ankylosing spondylitis is, you know, bamboo spine, you know what that is, OK. And you see, people are like this - the reason they can't straighten up is if they do the vertebrae will crack, it fuses together. And there was an experimental drug, it was on the market, that he got into a study on, but he had to take a shot once a week for $5,000 a shot. He was an attorney general of a state making $102,000 a year - a lot of money. But he was, that's what he had to pay $5,000 a week until it got approved, and then it went on the market, and it was able to go on the market at a reasonable price.”

The former vice president concluded - at that point he'd been standing at the microphone for more than an hour - by telling the crowd, “There's a lot more to say. . . . And my staff's going to kill me because I'm keeping you here so long.”

The Biden campaign declined to talk about the greater strategy behind the candidate's briefer speeches and declined to say whether this is the Biden voters will see for the rest of the primary contest and, if he makes it, the general-election race against Donald Trump.

However, the new approach may be more in line with what at least one powerful ally wants to see. A few days before the South Carolina primary, during a meeting on a World War II-era battleship docked near the city of Charleston, house majority whip James Clyburn offered a critique of his longtime friend's campaign. Included in it were worries that Mr Biden's speeches were too meandering.

“I said, 'There's a reason preachers deliver their sermons in threes. You know - Father, Son and Holy Ghost,' ” Clyburn recounted telling Biden. “Zero in on how to make this personalised, talk about their families, and talk in terms of people's communities.”

“I got it,” Mr Biden replied, according to Mr Clyburn, whose endorsement later that week helped propel Mr Biden to a momentum-changing victory in South Carolina.

Mr Biden is not the first candidate to institute a rhetorical course correction this campaign season. Late last year, Elizabeth Warren scrapped her 45-minute speeches, choosing instead to focus on a town hall format. In April, as the spotlight began to dim on Beto O'Rourke's presidential campaign, the former Texas congressman sought to add more substance to his stump speeches. He also stopped standing on countertops.

Most voters who hear Mr Biden's stump speech are experiencing it for the first time and are thus unaware of the newly abbreviated nature of his remarks. But the newfound brevity has not gone unnoticed by the campaign of the man who remains Mr Biden's chief obstacle for the Democratic presidential nomination.

On Saturday, Mr Sanders' campaign manager Faiz Shakir responded to a tweet that mentioned just how short Mr Biden's remarks had been by launching into his own comparative critique - apparently aimed at showing how much stamina Mr Sanders has, as well as the senator's ability to speak at length without mistakes.

“Bernie has three public events just today in two different states,” Mr Shakir tweeted, “each speaking engagement extending for close to an hour.”