After three years of near total silence, former US president Barack Obama has suddenly surged back into the spotlight in recent weeks, courtesy of an increasingly nasty spat with his successor Donald Trump.
It started on Friday, May 8, when Obama privately criticised Trump's response to the coronavirus pandemic, calling it a "chaotic disaster". His remarks were subsequently leaked to the media.
Trump has spent the 11 days since then raging about the man he replaced in the White House. Using every avenue available – media briefings, TV interviews and of course, social media – the President has labelled Obama "incompetent" and "corrupt".
He's also hyped up the "Obamagate" conspiracy theory, accusing Obama of committing "the biggest political crime in US history".
So far, what I've described is mostly one-way. Obama chided Trump in private. The President responded by going nuclear in public. All he got in return was single word.
That imbalance ended on the weekend. In a video message to graduating high school and university students, Obama launched a very public broadside against Trump.
In the process, he broke a longstanding, unwritten rule of American politics.
"More than anything, this pandemic has fully, finally torn back the curtain on the idea that so many of the folks in charge know what they're doing," Obama told the students.
"A lot of them aren't even pretending to be in charge.
"Doing what feels good, what's convenient, what's easy. That's what little kids do.
"Unfortunately a lot of so-called grown-ups, including some with fancy titles and important jobs, still think that way. Which is why things are so screwed up.
"All those adults you used to think were in charge and knew what they were doing? Turns out, they don't have all the answers. A lot of them aren't even asking the right questions. So if the world's going to get better, it's going to be up to you."
• Donald Trump's feud with Barack Obama escalates after veiled criticism from former president
• 'Obamagate': Donald Trump accusing Barack Obama of 'biggest scandal in history'
• Barack Obama emerges as central figure in 2020 presidential race
• Covid 19 coronavirus: Barack Obama labels Donald Trump's coronavirus response 'absolute chaotic disaster'
Obama never mentioned Trump by name, but there was no mistaking his meaning.
Trump isn't "even pretending to be in charge". He has no idea what he's doing. He's a "so-called grown-up" with a fancy title, acting like a "little kid".
That was the message Obama was sending.
It might have been subtle by the standards we've grown so used to these past couple of years, when casually abusive presidential tweets posted in all-caps have become the norm.
But in the broader context of history, Obama's condemnation of Trump was an extraordinary public intervention.
AMERICA'S UNWRITTEN RULE
This sort of public feud between presidents is not normal.
There is an informal tradition in the United States that former presidents refrain from publicly criticising whoever currently occupies the White House.
In recent decades, presidents from both parties have actually taken that tradition even further by developing genuine friendships with one another.
George H.W. Bush was famously close with the man who beat him in the 1992 election, Bill Clinton. George W. Bush and his wife Laura are warm friends with the Obamas.
In a way, it's easy to understand. Few people on the planet truly know the weight of responsibility a US president must feel. Presidents have bonded over that shared experience, despite their differing politics.
It's a club of sorts. And an unwritten rule of the club is that once you leave the White House, you give your replacement clear air to get on with the job.
Trump's Republican allies already thought Obama had breached that convention when his private comments leaked 11 days ago.
The party's most senior member of Congress, Senate leader Mitch McConnell, issued a particularly scathing response to him.
"I think President Obama should have kept his mouth shut," McConnell said.
"You know, generally, former presidents just don't do that.
"I remember President George W. Bush and his father went right through eight years of Democratic administrations after they left office and kept their mouths shut, because they didn't feel it was appropriate for former presidents to critique even the president of another party.
"I think it's a bit classless, frankly, to critique an administration that comes after you.
"You had your shot. You were there for eight years. I think the tradition that the Bushes set up, of not critiquing the president who comes after you, is a good tradition."
That assessment felt overblown at the time. Obama had not criticised the President in public. Someone had leaked comments he made in private.
But that distinction no longer applies. Millions of people watched his commencement speeches on the weekend. It doesn't get much more public than that.
WHY SPEAK OUT NOW?
If breaking this unwritten rule is such a big deal, the natural question to ask is why Obama decided to do it.
The most obvious explanation is that he is trying to help his former vice-president Joe Biden, now the Democratic nominee for president, win November's election against Trump.
The leaked remarks that sparked all of this came from a call between Obama and his former officials and staffers, during which he tried to convince them to fall in line behind Biden.
And there is every reason to think a prolonged public argument with Obama would be politically perilous for Trump. Polls consistently show the former president is the second-most popular political figure in the country, behind his own wife Michelle.
Every moment Trump spends fruitlessly attacking Obama is arguably a moment lost in his fight against Biden.
The other possible reason that Obama is speaking up? Well, that's simple. Trump provoked him.
The convention is that former presidents don't criticise current presidents, but that has never really stopped current presidents from criticising former presidents.
Obama did not shy away from blaming the Bush administration for his own political convenience during his early years in office.
Similarly, Trump has sought to shift some of the blame for his handling of the coronavirus onto the previous administrations.
And for nearly two weeks now, the President has been levelling incendiary accusations at Obama, centred around the latest iteration of his theory that Obama administration officials spent their last months in office trying to sabotage him.
"It is a disgrace what's happened. This is the greatest political scam, hoax in the history of our country," he said last week.
"People should be going to jail for this stuff, and hopefully a lot of people are going to have to pay.
"This was all Obama. This was all Biden. These people were corrupt. The whole thing was corrupt. And we caught them. We caught them."
At a media conference, he was asked to be more specific.
"What crime exactly are you accusing President Obama of committing, and do you believe the Justice Department should prosecute him?" a reporter asked.
"Obamagate. It's been going on for a long time. It's been going on from before I even got elected, and it's a disgrace that it happened," Trump replied.
"And if you look at what's gone on, if you look at now all of this information that's being released – and from what I understand, that's only the beginning – some terrible things happened, and it should never be allowed to happen in our country again.
"You'll be seeing what's going on over the coming weeks, and I wish you'd write honestly about it, but unfortunately you choose not to do so."
"What is the crime exactly, that you're accusing him of?" the reporter pressed.
"You know what the crime is. The crime is very obvious to everybody. All you've got to do is read the newspapers, except yours."
If someone accused you of committing the biggest political crime in history, you would probably be itching to respond.
BAD FOR THE COUNTRY
The spat between Trump and Obama is undoubtedly unedifying to watch at a domestic level, but it also has consequences for America's image overseas.
This week China leapt at the chance to portray the world's most powerful democracy as disorganised and beset by infighting.
The Chinese Communist Party's mouthpiece newspaper, The Global Times, used Obama's public criticism of Trump to gleefully mock its geopolitical rival.
"It's a tradition in the US that ex-presidents don't criticise a successor. It's rare for a predecessor to rebuke an incumbent president. But former president Barack Obama has violated the code of silence, criticising Donald Trump for mishandling the novel coronavirus epidemic repeatedly," it wrote.
"What made Obama break the longstanding tradition? The performance of the Trump administration amid the epidemic apparently is too poor to keep the former president silent. With over 1.4 million infections and nearly 90,000 deaths, it's fair to say the US coronavirus response is one of the worst in the world.
"Although Obama may also want to help Joe Biden, the Democratic candidate, win more support in the presidential campaign, his criticism of Trump's policy was more out of discontent with the grave epidemic situation in the US."
The paper also delighted in criticising Trump's obsession with the Obamagate theory.
"When the lives of more Americans are under threat from the novel coronavirus, the Trump administration has decided to devote much of their time hyping a conspiracy theory," it said.
"The purpose is clear – to discredit Biden by attacking Obama, and divert people's attention from its failures in dealing with the epidemic.
"With politics increasingly disconnected from reality, the US will only see more problems unsolved and be further mired in a crisis. This is the tragedy of US politics."
This was all a bit rich, coming from the authoritarian government that botched the initial coronavirus outbreak by trying to cover it up.
That said, the spectacle of two presidents feuding in increasingly bitter terms is indisputably ugly. It's not how the American system, with its strong emphasis on respect for the office of the presidency, usually works.