Before Joe Biden’s persistent gaffes raised concerns over his electability in 2020, they were causing headaches for his runningmate, Barack Obama.

In their 2010 book Game Change: Obama and the Clintons, McCain and Palin, and the Race of a Lifetime, John Heilemann and Mark Halperin noted the often tense relationship between Biden and Obama on the campaign trail.

The duo, who never warmed to one another, either as U.S. senators or presidential rivals, were thrown together on the Democrat ticket because each had something the other was lacking. Biden, for his part, provided the partnership with decades of experience in both the domestic and foreign policy fronts. Obama, although young and naive to the workings of the federal bureaucracy, had the charisma and authenticity that Biden’s two previous failed presidential bids had been missing.

The political union, however, was quickly tested as Biden’s penchant for gaffes, verbal missteps, and embarrassing comments played out in view of a national audience. The trouble began shortly after the Democratic National Convention in Denver, Colorado. Biden, who during the primary campaign had lambasted Obama as unprepared for the presidency, found old habits to hard break.

In mid-September 2008, Biden reportedly was “running his mouth” to reporters on his new campaign plane when he let it be known that he was more qualified to be president than Obama. The remark quickly soured relations between Biden, Obama, and their respective staffs, according to Heilemann and Haperin.

A chill set in between Chicago and the Biden plane. Joe and Obama barely spoke by phone, rarely campaigned together. Not only was Biden kept off Obama’s nightly campaign conference call, he wasn’t even told it existed. (When the idea of having Biden join was put to [campaign manager David] Plouffe, his response was ‘nah.’) A different daily call was set up for Joe, with [senior staff], so they could keep a tight reign on him.

The bitterness only escalated from there, especially as Biden began making more frequent gaffes on the campaign trail. In the final week of September alone, Biden “equated paying higher taxes with patriotism,” told voters both he and Obama were opposed to coal—contrary to their platform – and second guessed the campaign’s messaging strategy.

In the wake of such gaffes, Obama purportedly told his staff to “fix this problem with Biden,” but refrained from getting involved himself. All of that changed two weeks before Election Day, when Biden claimed at a fundraiser that Obama, if elected, would stare down an international crisis in his first six-months.

The prophesy would not have stirred much concern, except Biden gave the impression to those in attendance and the media that he was “showing off” for wealthy donors, and the crisis in question would be “generated.”

”Mark my words,” Biden told the crowd. “It will not be six months before the world tests Barack Obama like they did John Kennedy … Watch, we’re gonna have an international crisis, a generated crisis, to test the mettle of this guy.”

Biden’s remarks proved to be a red line for Obama, as Heilemann and Halperin detailed in their book.

On Obama’s nightly call, the candidate hit the ceiling. ([Chief strategist David] Axelrod was already up there, needing to be peeled off, having let fly a string of F-bombs when he first found out what Biden had said.) ‘Golly, man!’ Obama said, with more anger in his voice than ‘gollys’ normally carry. He was, in fact, as pissed off as most people on the call had ever heard him, more so than he’d been at even the wickedest jabs from Hillary Clinton. ‘How many times is Biden gonna say something stupid?’”

Publicly Obama attempted to clean up the gift his runningmate had just given Republicans, who had began running ads using the comments immediately.

“I think Joe sometimes engages in rhetorical flourishes,” Obama told The New York Times shortly after the incident.

Privately, though, Obama was livid and not afraid to express his feelings to Biden during a private call between the men, which was described to Heilemann and Halperin:

A couple of days later, Obama phoned Biden and laid into him. You were supposed to have my back, he said, not be out there creating problems…. More than that, though, what rankled Obama was that Biden hadn’t bothered to pick up the phone and apologize. Worse, Biden didn’t say that he was sorry when Obama called; he showed no remorse for his … comments or understanding that they posed a real political problem.

Despite the concerns, Obama and Biden went on to win the election by a substantial margin. There is some credence that Obama had cause to worry. National exit polls from the race showed the late Sen. John McCain (R-AZ), the Republican nominee, winning voters most concerned about “terrorism” by a margin of 86 percent to 13 percent.

The episode comes back into the spotlight as Biden’s own 2020 bid is weighed down by a surge of high-profile gaffes. In tur, such blunder, have reignited existing doubts from the left over Biden’s capabilities and fitness for the presidency.

Obama, himself, has granted credence to such doubts by not endorsing his former runningmate and refusing to defend him in the wake of a recent controversy involving Biden’s praise of segregationists. The true nature of Obama’s feelings were only further illuminated last week, when it became public the former president attempted to dissuade Biden from running.

“You don’t have to do this, Joe, you really don’t,” Obama told Biden before the 76-year-old formally launched his campaign in April.