Partisan politics is necessarily tribal, a blessing and a curse. The tribe provides friends, training, support — for some, jobs — and protection to its members. It also excludes, stereotypes and objectifies the other, behaviour essential to its identity. Its most valuable currency is membership, and the status and network it provides.

How generously it bestows membership, and to whom, is key to its politics, even to its survival. Make it exclusive and hard to get and you have the “vanguard” parties of left and right that led, in part, to the disastrous bloodshed of the 20th century.

Cheapen membership by giving it away, or allowing joint membership in several tribes and you weaken the meaning of joining, and therefore the institution itself.

Canadian Conservatives might want to reflect on this. They have allowed their members in four provinces to belong to several tribes. As a result, there is no branded Conservative choice for voters in any of them, in choosing a provincial government — the most important governments in Canada.

Liberals, too, might want to reconsider the wisdom of giving membership to anyone who clicks a checkbox on a website. Not only is their membership worth what you have not paid for it, it opens the tribe open to leadership-driven, fair-weather friends at best; usurpers, at worst.

New Democrats have struggled with this balance, too. The party that has always advocated social inclusion, a Canada open to all. But they have been too often, too little welcoming to newcomers to their own tribe. The party, as a result, became too old, too white and too affluent, before the Jack Layton renewal. His high-water mark has faded, and in the past five years donors and membership fell.

If Jagmeet Singh is to break through the Layton threshold, let alone vie for power, he must resolve this paradox at the heart of the NDP. His journey to date has been impressive, even spectacular, but the next chapters will be harder.

Jagmeet’s leadership campaign demonstrated his ability to organize and to mobilize, especially among those who had not previously been engaged in politics. Now he needs to show that these were not just one-time leadership campaign recruits. His goal should be to build on that base to reach a level of 250,000 or more party members, roughly the level the Liberals claim.

To cynical veterans this seems improbable. That is what their cousins in the U.K. said while Jeremy Corbyn multiplied the Labour Party’s numbers more than fourfold, to become the largest political party in Europe, or when Bernie Sanders developed an online following in the millions in a few months. The NDP had nearly 200,000 members 30 years ago. Yes, these times are different, but the Corbyn/Sanders/Macron examples show that it can be done today.

The corrosion of the institutional foundations of parties, the secular weakening of their organizational sinews, among most of the once most powerful on left and right is not a partisan issue. It is an issue of the health of liberal democracy itself. Strong local political parties are the foundation of stable democracy.

A party whose pre-election membership doubles or triples and then crashes, has few real assets. It has little ability to deploy its members as advocates on an important issue — they are too busy paying off debts and trying to hustle replacement members.

Singh can align the NDP’s internal culture and behaviour with its public stance of openness and inclusion, and bring in tens of thousands of new members. He can build a party like that of an Obama, Sanders or Corbyn. If he does, he can use this new machine of younger, more diverse, passionate Canadians to deliver his message on millions of doorsteps and Facebook pages.

In 2011, Layton did so well in part because the Liberals campaigned so badly and were so poorly led — and because he had built a new party. In 2015, Justin Trudeau did so well because the Tories and the NDP both campaigned so badly and were equally poorly led. He, too, had built a new Liberal party.

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Given that Andrew Scheer is new and inoffensive and that the Tories have a strong base, they are likely to recapture some of the Harper coalition. But if Singh is able to continue the party growth he has begun, to build a new party made up of passionate activists in every region of Canada, he may make 2019 the first genuine three party horse-race in many decades of Canadian history. Stay tuned.

Robin V. Sears, a principal at Earnscliffe Strategy Group, was an NDP strategist for 20 years.

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