It had all been going so well.
The serious political business of the day dispensed with, Joe Biden left Belfast and broke for the border.
Arriving for the first day of ancestral exploration in County Louth, he was taken on a tour of Carlingford Castle, the last sight his great-great-grandfather Owen Finnegan would have seen in 1849 as he sailed away to a new life in America.
The rain sheeted down, the cold was something from the depths of winter.
And yet, the 80-year-old president exuded an energy of a much younger man, beaming from beneath his baseball cap as he arrived in Dundalk.
Traditionally a staunchly republican border town, he wound up at a bar improbably called The Windsor.
Here, in relaxed mood, he spoke from the heart, and apparently off the cuff.
And that’s where the gaffe came from.
He was paying tribute to his distant cousin in the room, the former Irish rugby international Rob Kearney.
Kearney was a member of the Irish team that famously beat New Zealand’s All Blacks for the first time ever, in a 2016 match played in Chicago.
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President Biden, who played rugby himself as a student, said that Rob Kearney was “a hell of a rugby player, and beat the Black and Tans”, thus confusing New Zealand’s famous team with the reviled British paramilitary force the Black and Tans, who brutally repressed opponents of British rule during the Irish War of Independence.
Most infamously, the force massacred 14 people and wounded 60 more at a Gaelic football match at Croke Park in Dublin in 1920.
It seemed an obvious slip of the tongue, rather than anything intentional.
But here you had a US president often accused by unionists of being rabidly republican, apparently bragging about his family beating the British. In that context, the remark was deeply unfortunate.
President Biden continues on a more familiar political path on Thursday, meeting with the Irish president and prime minister, and addressing the Irish parliament. We can expect his comments there to remain more rigidly to script.