Elections often turn on a few carefully crafted sentences – a “campaign narrative” that tells voters why they should say yes to a candidate. If Justin Trudeau nailed this in 2015, things will be a lot tougher in 2019. Last week he offered a clue as to what the new narrative might say.After shuffling his cabinet, Trudeau used his press conference to rebuke conservatives around the world for engaging in “the politics of fear and division,” which he condemns as “a very dangerous game.”Now, fear mongering is hardly confined to conservatives, but Trudeau is dead right about the trend. It's there and it's deeply damaging to politics and policy. If debate is supposed to be a contest of ideas, increasingly, the cynical alternative is to incite anger and division.Take Donald Trump. His plan to Make America Great Again is nothing of the sort. It is about making ordinary Americans mad at the world, from Washington “elites” (Drain the Swamp!) to Latinos (Build the Wall!) to Canadians (Tear up the Agreement!).Trudeau believes strong voices can prevail over this kind of politics and promises that his cabinet will work to unite rather than divide Canadians. Coming on the heels of a shuffle and heading into an election year, this certainly sounds like a signal of things to come. So, how will Liberals respond to the politics of fear? What can they say?They will need a narrative – a story. At bottom, it will be about trust, openness, and cooperation because that is the right answer to the politics of fear, but there are different ways to frame the story. The circumstances for 2019, I think, call for something unusual: an allegory, that is, a story with messages on multiple levels, including an important lesson for Canadians. Let me explain.First, campaign narratives usually include one or two core challenges that the government plans to address. In 2015, for example, it was to rebuild the middle class. This time round, it should be sustainable development.This may raise eyebrows. After all, that is ground zero for what look like some very divisive battles leading up to the election. On carbon pricing, provincial opponents like Doug Ford, Scott Moe, and possibly Jason Kenney are already itching for a fight. Other provinces may be ready to join in.Then there's the pipeline, which promises some messy, angry, highly visible confrontations with protesters, First Nations, and the BC government.Nevertheless, this is a battle Trudeau seems ready – perhaps eager – to wage. I can think of at least two reasons why.Frist, nothing on the table has even close to the same potential for a major policy win. We had a brief glimpse of this in the first half of the mandate when the provinces and industry seemed ready to commit to carbon pricing. A pipeline too seemed within reach.Had the package come together, the Liberals would have redefined a big piece of the policy landscape. And this would have ushered in a new, long-term trend in policymaking that, as a political achievement, would have rivaled Medicare or Free Trade. But can the Liberals win on this issue in 2019?This brings us to the second reason. Sustainable development is the perfect allegory for the other battle Trudeau wants to wage, the one against the politics of fear – and Donald Trump is the perfect foil.American politics is spinning out of control and the stakes are rising daily. Even the coolest heads seem convinced that something basic is breaking down – that democracy really is at a crossroads and that authoritarian politics may be rearing its ugly head.The 2019 election campaign will be played out against this backdrop. Seen from this angle, sustainable development is much more than a policy goal, it is a beacon of hope. It not only teaches that prosperity and environmental stewardship can work together, it sets new rules for how policy debate works.Sustainable development is about balancing these two goals – and that is the opposite of a winner-take-all contest. It starts from the assumption that issues don't exist in isolation. They are interconnected. Debate is all about exploring these interconnections, then working toward solutions that balance different interests. And this must be done together.So, when opponents of Trans Mountain or carbon pricing call on Canadians to take their side against the other, Trudeau should reply that they misunderstand the issue: jobs, the environment, Indigenous rights, and engineering options are variables in a complex equation that must be solved together.Would Canadians buy it? Normally, people have a low threshold for complex ideas, but these are not normal times. Trudeau would be gambling that Canadians have had it with political tribalism. They see that it is all take, no give. And they know that complex issues won't be solved unless everyone puts some water in their wine – which brings us to the allegory.Sustainable development is the adult answer to political tribalism. In the current context, it will stand as a challenge to every citizen to make a choice; not between jobs and immigrants, or the economy and the environment, but between anger and openness, between lashing out and working together.So, at one level, the campaign narrative would be a story about solving difficult issues in a new way; but at another it would convey a deeper, urgent message about the state of our politics and the responsibilities of democratic citizenship. But it stakes out this higher ground without moralizing.If politics is a contest between two primal emotions – hope and fear – Trudeau may have an opportunity to craft an historic narrative that will stand as a kind of Rubicon, separating those who peddle fear from those who offer hope.Dr. Don Lenihan is an internationally recognized expert on public engagement and Open Government. He is currently advising The Ottawa Hospital on an engagement plan to develop its new Civic Campus – a $2 billion, 10-year project. He also co-chairs the Open Government Partnership's Practice Group on Open Dialogue and Deliberation. Don can be reached at: [email protected] or follow him on Twitter at: @DonLenihan