If Joe Biden wanted to design a pair of gaffes to cause his presidency as much damage as possible, it would be hard to do better than his performance on Thursday night.
This Nato summit in Washington has already been overshadowed by questions about the US president’s age and mental capacity, and every world leader has been asked about it in interviews here.
Two miles away, on Capitol Hill, Democrats have been locked in conclave all week to discuss what to do about Mr Biden and his health.
All eyes were on this evening, to see if he could bring this summit to a close without a hitch. He could not.
There was a gasp in the media centre, where hundreds of journalists were gathered to watch that press conference.
On screens around the room, Mr Biden turned to his left and prepared to give way to Mr Zelensky.
“And now I want to hand it over to the President of Ukraine, who has as much courage as he has determination,” he said.
Pausing for effect, he concluded: “Ladies and gentlemen – President Putin.”
Immediately, the atmosphere among the assembled hacks turned from one of interest, to one of horror.
The feeling in the room was exactly the same as at the presidential debate on June 27, when Mr Biden froze on stage. People looked at each other as if to say: “Can this really be happening?”
Sir Keir Starmer, Olaf Scholz and Emmanuel Macron were all asked about it in their own press conferences minutes later, and all dismissed Mr Biden’s mistake as a harmless slip of the tongue.
But the truth is that the timing of this incident could not have been more unfortunate.
But an hour and a half later, he did it again. In his own press conference, Mr Biden was asked about Kamala Harris’s suitability to be president, in an obvious nod to the idea of her replacing him on the Democratic ticket.
“I wouldn’t have picked Vice President Trump to be vice president, if she’s not qualified to be president,” he said. More gasps, as the penny dropped that he had mistaken his closest ally for his greatest foe.
Mr Biden struggled as he explained that the Nato press conference was the most successful in a “long time”, and that other world leaders had credited him with bringing them together.
His own speech was unusual for a world summit. It focussed on the differences in his foreign and domestic policies from those put forward by Trump.
At one point he started talking about US inflation figures ─ putting himself in full campaign mode ─ in an attempt to get on the offensive after his own mistake. He said Trump was a threat to the Nato alliance.
It does not feel that will be enough.
With unprecedented pressure on his campaign from fellow Democrats, Mr Biden’s team have been hoping that this week’s summit was a chance to show his “big boy” credentials.
He was meant to turn up and play his favourite role: the man saving the world from Russia, and preventing a second term of what he calls Donald Trump’s “unhinged” agenda.
He did speak at length, with no notes, about foreign policy and America’s relationship with China, Russia and South Korea.
That performance attracted praise in some quarters, from Democrats who saw the old Biden shine through.
But with his ridiculous errors on the names of some of his closest allies, he risked making America look like an international joke, and left Western leaders scrambling to cover for him.
It is almost certain that tonight’s events will see more Democrats come forward to declare they cannot support his campaign any longer.
He was insistent he would not stand down, and this campaign will only end when Mr Biden decides to end it.
But if Mr Biden looked shaky at the start of this week, tonight he looked finished. The coming days will be dark indeed.
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