It wasn't the moustache. It wasn't the smile. It wasn't even the cane.
The rise of Jack Layton and the NDP has systematically dismantled the conventional wisdom underpinning this election campaign. That the NDP and its ailing leader would be easy pickings for the Liberals. That the Bloc Québécois would tighten its grip on Quebec. And, most particularly, that the Conservative Party would not need to fight a national election, and could instead focus on snatching a handful of seats to secure a majority on Monday.
In explaining the sudden growth of the NDP in polls, much has been made of Mr. Layton's personal appeal. And it is considerable, especially when compared to his rivals. Stephen Harper has been dour, his sharp sense of humour stowed away for the duration of the campaign. On the campaign trail, Michael Ignatieff has been fiery - but not warm.
Contrast that to Mr. Layton, beaming now, more than ever. With the mustache, part of the image that makes him the candidate Canadians would most want to grab a beer with. And the cane, a subtle but constant reminder of his perseverance and a validation of his stump speech that he is a fighter.
Yet, it would be a mistake to ascribe the NDP's rise to Mr. Layton alone, and a mistake to think Mr. Layton's appeal springs only from his sunny disposition.
To understand the surge of Jack Layton and the NDP, you must first understand this: there has not been a surge. Or at least not just one. Instead, the rise of the NDP during the 2011 election campaign has come in stages, even though the results - and the possible startling electoral consequences - have only truly become visible over the past week.
The first stage was the early collapse of the Green vote. For EKOS pollster Frank Graves, the decline of Elizabeth May's party was an early wave of strategic voting, with former Green supporters deciding they needed to back candidates that could get elected.
Then came Quebec. The NDP was showing signs of life even before the leaders debates, something that Gilles Duceppe had seemingly realized by the night of the English-language contest. His attempt to corner Mr. Layton on Bill 101, so puzzling at the time, makes perfect sense now. The Bloc leader was trying to squash the NDP leader's appeal among left-leaning soft nationalists.
Mr. Duceppe failed, epically. He compounded that failure with ill-timed boasts of a renewed push for a sovereignty referendum at the Parti Québécois convention the weekend after the debates. That week, the NDP began to rocket upward in Quebec. Asked to choose between hope and stale, stark division, Quebeckers went with the smile and the mustache, not to mention the suitably vague promise of constitutional change.
All of that was enough to push the third-place NDP close behind the Liberal Party, and spur warnings that a split left-wing vote would deliver at least 155 seats to the Tories, enough for a majority government. In past elections, that warning has been enough to herd a sufficient number of progressive people - Starbucks voters - into the Liberals' arms. Those voters might not love the Liberal Party, but their dislike of the Conservatives overcame any philosophical hesitations.
But not this time. The New Democrats were too close; close enough, in fact, that NDP supporters discovered that their hearts and heads were pointing at the same ballot choice for once. Even worse for the Liberals: The old argument about not wasting a vote on the third-place party has begun to turn against them. Those voters, defecting from the left wing of the Liberal Party, are the group that has helped to push NDP support to undreamt-of levels, within striking distance of the Conservatives.
There is one unexpected group that Mr. Graves sees as being the latest to alight on the Layton bandwagon: disaffected Conservatives, who, years before they were Tim Hortons voters, supported the NDP.
Mr. Layton's blended appeal of personal populism and pocketbook promises has seemingly drawn from both the Tim Hortons and Starbucks pools of voters - a Tim Hortons latte campaign that has led his party to the brink of an unprecedented breakthrough.