The only question is whether he can be nipped at the wire.
Inside bettors suggest probably not. But the NDP's complicated process for selecting a successor to the late Jack Layton makes it difficult to handicap the outcome with any confidence, even at this late stage.
Whether any of his six rivals can beat the Montreal MP to the finish line Saturday depends on a host of unpredictable factors, including how many of the 131,000 eligible New Democrats actually vote, how far ahead Mulcair is on the first ballot, the order in which trailing contenders drop off the ballot and whether their supporters move primarily to one candidate or scatter.
Most difficult to predict are the individual choices tens of thousands of New Democrats are making — in the privacy of their own homes, free of the group think and the hoopla of Saturday's convention in Toronto — as they mark their ballots.
As of Wednesday morning, 43,000 had voted in advance, online or by mail, ranking their preferences from first through seventh. Assuming a high voter turnout of 70 per cent, that means almost half had voted early, with tens of thousands more ballots expected to pour in until advance voting is cut off at 11 a.m. ET Friday.
With advance preferential ballots, a voter's first choice will be counted until that candidate is dropped from the ballot, at which point the voter's second and subsequent choices will be counted until one contender emerges with more than 50 per cent of the votes.
An unknown number of additional online voters, as well as the roughly 3,000 who've registered to attend the convention, will vote ballot by ballot in real time, starting Friday night and continuing Saturday.
Long shot candidate Martin Singh, a Nova Scotia pharmacist, is the only one who has attempted to openly direct his supporters — to Mulcair — once he's scratched from the ballot. The other contenders haven't bothered, deeming it a futile exercise akin to herding cats.
New Democrats revel in their reputation for contrarian independence; they don't like being told what to do. And they have regional preferences when it comes to second choices that don't necessarily equate with what their first-choice candidate would like them to do.
Former party president and veteran backroom strategist Brian Topp, for instance, has positioned himself as the anti-Mulcair candidate and is seen to be most ideologically attuned with Toronto MP Peggy Nash. Yet his Quebec supporters are most likely to switch to Mulcair if Topp is knocked off the ballot.
Indeed, various camps privately admit the purported ideological divide among the candidates — the allegedly more centrist Mulcair and Nathan Cullen versus the more traditionalist Topp, Nash and Paul Dewar — has been exaggerated for the purposes of sharpening distinctions during the campaign. And it's not likely to play as big a role in determining second choices as many pundits have suggested.
"This is not (a choice between) left-right, no matter what the pundits say," says a strategist with one camp. "This is all about who can win."
Having vaulted into official Opposition status for the first time last May, New Democrats are determined to hang onto their historic gains in Quebec and expand their reach elsewhere. First and foremost, they are looking for a leader who can make the leap into government in the next election in 2015.
Fear that their Quebec surge is already ebbing away has helped propel Mulcair, a former Quebec Liberal cabinet minister and the only contender with any profile in the province, into the lead. And it will likely ensure that his main competition come Saturday will be Topp, the only other candidate with any credentials in the province, where he was born and raised.
As they head down the home stretch, only Mulcair, Topp and Cullen, an MP from northern British Columbia, appear to have any momentum. They're ranked one, two and three in terms of fundraising, they've dominated the air war in the final days of the campaign and they each have strong support in B.C., the province that is home to almost 40,000 card-carrying party members, almost a third of the total eligible voters.
Singh and Manitoba MP Niki Ashton are trailing the field and Nash and Ottawa MP Dewar, once considered among the top tier of candidates, seem to have stalled.
Insiders still give Nash an outside shot at becoming the compromise choice, provided that she's ahead of Topp and most of his supporters eventually switch to her. However, Topp is finishing the race more strongly than the risk-averse Nash, propelled in part by the controversial 11th-hour intervention by former NDP leader Ed Broadbent.
Broadbent, who endorsed Topp at the outset, last week openly questioned the mercurial Mulcair's temperamental suitability for the job of consensus-seeking team-builder, accused him of taking undue credit for the party's breakthrough in Quebec and of wanting to turn the social democratic NDP into another centrist Liberal party.
Rival camps concede the tactic has likely helped Topp — the first out of the gate and initially the presumed front-runner — consolidate the anybody-but-Mulcair vote. But it may also have limited Topp's potential to pick up second choice support, turning off New Democrats who fear for the long-term unity of their party.
As for Dewar, his inability to converse fluently in French has likely fatally wounded his hopes for coming up the middle.
Dark horse Cullen would seem a natural compromise choice. He's vaulted himself from the ranks of the also-rans into real contention almost entirely on the strength of his engaging manner and sunny disposition. Other than slamming Singh for calling Topp a liar, he's taken pains to run a positive, upbeat campaign, saying nothing that could alienate the supporters of other candidates.
But it's an open question whether Cullen's late-blooming "little campaign that could," as campaign manager Jamey Heath has dubbed it, has the organizational muscle to get its vote out or will be able to rely instead on the self-motivation of his supporters.
Even if they turn out in force, Cullen has tied an anvil to his campaign that will make it hard, if not impossible, to surge past the front-runners: his proposal to have Liberals and New Democrats field joint candidates in Tory-held ridings. He's defended the idea, aimed at ensuring the defeat of Stephen Harper's Conservatives in the next election, with spirit but it remains unpalatable to many New Democrats.
Where Cullen's supporters will go if he's knocked off the ballot is a big wild card in the contest.
Pundits have suggested Cullen and Mulcair are natural allies, both representing change and hoping to widen the NDP's tent. Yet many of Cullen's supporters joined the party specifically to support his plan for pre-election co-operation with the Liberals, an idea every other candidate has flatly rejected, none more vehemently than Mulcair.
Indeed, Mulcair has gone further than any of the others in categorically ruling out co-operation with the Liberals under any circumstances.
Just as plausibly, Cullen's supporters could simply scatter to a variety of candidates or they could just opt not to vote for anyone else at all.
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