WASHINGTON - It takes only an instant chatting with Justin Trudeau about other world leaders to establish that he carries an unusual inventory of memories for a rookie prime minister attending his first international summit.
He's already met three U.S. presidents — Barack Obama will be the fourth. And at the G20 summit that begins Sunday, should he offer condolences to Germany's Angela Merkel on the passing of her predecessor Helmut Schmidt, he could include a childhood anecdote about meeting him too.
It turns out that being the son of a four-term prime minister produces so many anecdotes about world leaders it's impossible to keep track of them all.
When asked, for instance, about the time a former U.S. president predicted he'd be prime minister some day, not only had Trudeau never heard the story — he couldn't guess which president it was.
''Was that Jimmy Carter saying nice things?'' Trudeau said, in a June interview with The Canadian Press.
Given that Richard Nixon's light-hearted prediction turned out to be accurate, the anecdote has recently been published in international news reports. But when informed earlier this year of Nixon's now-prophetic toast at a state dinner in 1972, Trudeau replied: ''Oh, my goodness.''
He never met Nixon but he could reminisce about several other of Obama's predecessors. Like the time Ronald Reagan read poetry to him as a kid. Or about Bill Clinton's 60th birthday bash. Or Jimmy Carter meeting Fidel Castro at his dad's funeral.
He might have met a fourth and fifth U.S. president — but neither of the Bushes were home when Trudeau and his dad, during a vacation in Maine, dropped in to visit Barbara at the family compound in Kennebunkport.
He also went to Leonid Brezhnev's funeral in Russia; met Margaret Thatcher; and treasures a hunting knife given to him by Olof Palme, the Swedish leader who was later assassinated.
So he begins his international career with an uncommon reservoir of conversation material. It's a useful asset for someone whose stated view is that personal connections are a vital part of foreign relations.
"One thing I learned from my father about international relations is they're about relationships," Trudeau said in that June interview.
It's a point repeated in his book, "Common Ground." He writes about hearing his father's briefings before international meetings and being struck by how much they were about people — not just topics like arms control and trade deals: "(They) were often as much about the personalities of his counterparts as about the issues."
Leaders with very different personalities can succeed at bonding, the book argues, citing a childhood memory about an unprecedented level of security around Trudeau's childhood home one day in 1981.
A famous visitor was coming to 24 Sussex Drive. And then, during his first foreign trip as U.S. president, Reagan read him a poem about the rugged Canadian north.
Contemporary newspaper accounts refer to Reagan reading Robert Service's "The Cremation Of Sam McGee." Trudeau recalls it being "The Shooting of Dan McGrew." In any case, he writes about being thrilled by the slightly mature subject matter and the fact it was unlike the poems preferred by his classics-loving dad: "I was impressed enough to memorize it."
Of course, old anecdotes will only impress his interlocutors for so long.
Even before tragedy struck in Paris and cast its shadow over upcoming international summits, it was clear Trudeau would be confronted with concerns about counter-terrorism.
The White House has already signalled two questions it intends to raise with him: One involves Canada's role in fighting ISIL, another is whether Trudeau will continue co-operating on domestic national-security programs.
Obama spokesman Josh Earnest told a briefing last week: "That counter-terrorism relationship has been important to our national security. It's one that we want to ensure continues."
Trudeau appeared aware, in that meeting five months ago, that the issue could become an irritant. He immediately interrupted a question that suggested he might withdraw from the U.S.-led coalition against ISIL.
''No, no, no, no, no. Sorry. Stop right there," he interjected.
"I have been unequivocal that Canada should be part of the mission against ISIL — that Canada does have a role to play as part of the coalition. I've just been in disagreement with (the Harper) government that the bombing-combat mission is the best thing that Canada can do to help."
And should they seek a break from discussing the gravity of global affairs, there's another light conversation topic the U.S. president will undoubtedly find relevant as the father of two teens and his presidency nearly over: what it's like for a kid to grow up in an official residence, and then leave for the outside world.