CHICAGO (NYTIMES) - It started with a photograph - the shot retweeted round the world, if you will.

Snapped aboard United States presidential hopeful Hillary Clinton's campaign plane late on Saturday (Oct 22) night by her traveling press secretary Nick Merrill, the picture captured Mrs Clinton staring at a smartphone, mouth agape in astonishment, as she watched the Chicago Cubs clinch a World Series berth.

Mr Merrill posted the picture on Twitter at a little after 11. "That look when you cap off a day on the trail by watching the @Cubs cement their trip to the #WorldSeries," he wrote.

Almost instantly, the image ricocheted across social media - and kicked up a heated debate, one that cuts to the heart of the character and integrity of the Democratic presidential nominee: Was Mrs Clinton, a native Chicagoan who ostentatiously donned a New York Yankees hat during her 2000 campaign for the Senate from New York, really a Cubs fan at heart?

Or was she a baseball flip-flopper, cynically falling in behind whichever team was more advantageous in an election year?

The evidence was soon being parsed more carefully than her record on free trade.

An indictment was quickly circulated, and in one of Mrs Clinton's hometown papers, no less. (Or, shall we say, in one of the Chicago papers.)

"It's time to recount Hillary Clinton's tortured explanations about being a die-hard Cubs fan - and how she's also for the Yankees," Ms Lynn Sweet, a Sun-Times columnist, had written in a piece published last Thursday.

And yet the fact of Mrs Clinton's Cubs fandom is not really open to dispute.

Born in Chicago in 1947 - two years after the team last appeared in the World Series - Mrs Clinton grew up in the suburbs, watching the Cubs on television with her brothers. They even re-enacted plays from the games, according to a newspaper column she wrote in spring 1996.

Her father was a devoted fan, too, making her loyalty both geographic and genetic.

"Even when baseball has tested my patience and allegiance, I've always managed to hold on to my soft spot for the Cubs," she wrote.

The source of suspicion as to Mrs Clinton's baseball loyalties is another set of facts: In 1999, only days after announcing that she was forming an exploratory committee to run for the Senate from New York, she and her husband, then President Bill Clinton, welcomed the Yankees to the White House for a visit. Mrs Clinton donned a Yankees cap given to her by the team's manager Joe Torre.

The resulting photographs fueled scorching criticism for years.

"She went to the Yankees so that she could run for senator from New York," Mr Chris Matthews said in 2007 on MSNBC's Hardball. "It's so obvious. Why is she - doesn't she know she looks like a fraud?"

In her defence, Mrs Clinton has pointed to ample evidence, including interviews from the early 1990s, that as a young girl in Chicago, she followed the Yankees in addition to the Cubs because she "needed an American League team", and "in our neighbourhood, it was nearly sacrilegious to cheer for the rival White Sox", as she wrote in her 2003 memoir, Living History.

As a seven-year-old, Mrs Clinton recalled in a speech in 2011, she dressed up as Mickey Mantle for Halloween, adding, "I have the picture to show you and to prove it."

And in a lengthy 2007 profile, Growing Up Rodham, the respected Washington Post sports columnist Sally Jenkins corroborated this claim: "By age 10, Hillary was a tomboy obsessed with baseball, especially the switch-hitting Mickey Mantle."

Claims and counterclaims about baseball fandom are almost inescapable in presidential election years, when the campaign inevitably bumps into the baseball postseason. Candidates are pressed to express a rooting interest - ideally with a plausible pre-existing explanation.

And yet these are treacherous waters to wade into.

In 2004, then presidential hopeful John Kerry made the mistake of linking his candidacy's fate to that of his beloved, World Series bound Boston Red Sox. He compared himself to the team's lights-out closer Keith Foulke and vowed to disprove the notion of any "curse" on either him or the Sox.

The Red Sox won. Mr Kerry did not.

At least no one could accuse him of national pastime pandering. The same cannot be said of other presidential candidates.

In 2008, then presidential hopeful Barack Obama told an audience in Philadelphia that because his Chicago White Sox had been knocked out of the playoffs, he was going to root for the Phillies against the Tampa Bay Rays.

Not 10 days later, he joked with an audience in Florida that he was thinking about getting a mohawk, a trend at the time among hardcore Rays fans.

His opponent John McCain pounced: "It's pretty simple, really. When he's campaigning in Philadelphia, he roots for the Phillies, and when he's campaigning in Tampa Bay, he shows love to the Rays."

Mrs Clinton's dual loyalties, longstanding and verified or not, may be an affront to baseball purists, who believe that a true fan can have only one team. And some of today's Cubs fans may not feel that she deserves to share in their celebrations.

But there is no mistaking the look of bliss on Mrs Clinton's face in that photograph taken aboard the campaign plane. As any sports fan can attest, it is a state that not even the most gifted politician can manufacture.

Besides, if the goal was to pander to voters, she would be far better off rooting for the Cubs' swing-state opponents - the Cleveland Indians.